Comparison

J vs ShiftRhythm

Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.

Head to head
About

J

This app provides tools to structure your juggling practice sessions, including warm-up, practice, and cool-down routines. It features interval training for customized workouts and a talking timer for endurance practice, offering verbal feedback without needing to check your stopwatch.

Highlights
  • Structured practice routines (warm-up, practice, cool-down)
  • Customizable interval training workouts
  • Talking timer for endurance practice
  • Verbal feedback for endurance contests
  • Ad-free experience
Features
Read full description

Enhance your juggling practice! The J-Trainer app will give you tools to ensure that your juggling practice sessions include proper warmup, practice, and cool down. The interval training portion of the J-Trainer tool allows you to build customized workouts to ensure you spend the right amount of practice time on each section of your practice. Most juggling festivals include endurance contests like: club balance endurance, 5 ball endurance, 5 club endurance, and quarter juggling endurance. The Talking Timer feature of the J-trainer gives you verbal feedback on your endurance, so you don't have to look down at your stop watch. ---------------------------- No advertisements and no in app purchases are contained in this app. ---------------------------- Other apps by this developer: Protect TD (Protect Tower Defense - Save the Animals) Math Tower Defense Eagle Mandarin Mandarin Prof Math Town Spelling Ace Spy Town Spanish Prof ---------------------------- I hope you enjoy this app. Feel free to send me feedback if you have suggestions for future updates.

About

ShiftRhythm

This app helps night shift workers optimize their sleep and light exposure based on their unique roster. It provides personalized guidance for sleep, naps, and light timing to align with your body clock and manage sleep debt.

Highlights
  • Personalized sleep and nap timing
  • Light exposure guidance
  • Circadian rhythm dial
  • Sleep score and debt tracking
  • Roster presets and custom schedules
  • Apple Watch app and widgets
Features
Read full description

Night shifts flipped your sleep? Enter your roster and ShiftRhythm tells you when to sleep, when to nap, and when to seek or avoid light — today. WHAT IT DOES • 24-hour body-clock dial — see your estimated melatonin onset (DLMO) and biological night (CBTmin) at a glance • Light, nap & caffeine guidance — timed to your circadian rhythm and updated as your shifts change • Sleep score, sleep debt & recovery — last night's sleep plus HRV and resting heart rate from Apple Watch, telling you whether to push or recover • Presets that match real rosters — Panama 2-2-3 schedule (day/night), Pitman, DuPont, Fire 48/96, 12-hour rotating shifts, plus Korean and Japanese patterns. Or build your own custom rotation • Melatonin timing card (optional) — an informational window based on your estimated body clock. Not a recommendation to take melatonin; talk to your doctor or pharmacist first BUILT FOR SHIFT WORKERS Whether you're a night shift nurse, a firefighter on 48/96, a plant operator on a DuPont rotation, or a driver on a rotating roster — ShiftRhythm adapts to your schedule, not the other way around. • Tap any calendar day to correct that day's shift • Works from your schedule alone — no Apple Watch required • Apple Watch app and widgets included; available in English, Spanish, Korean, and Japanese PRIVATE BY DESIGN • No account. No server. Your data stays on your phone. • All circadian math runs on-device — health data never leaves your iPhone • No ads, no tracking PRICING • 30-day free trial — full features, no account needed • Then Monthly or Annual (Annual saves vs. monthly), or a one-time Lifetime purchase if you'd rather not subscribe • Subscriptions auto-renew; cancel anytime in Settings > Apple Account > Subscriptions Terms of Use (EULA): https://www.apple.com/legal/internet-services/itunes/dev/stdeula/ Privacy Policy: https://yoonspower.github.io/shiftrhythm/privacy.html ShiftRhythm is for general wellness and reference only. It is not a medical device and does not diagnose, treat, or monitor any medical condition. Values shown are estimates and may be inaccurate. Consult a professional for health concerns.

Screenshots

J4 screens
ShiftRhythm4 screens

Verdict

The call

The clearest difference is in-app purchases: J at none against ShiftRhythm's 3. J also leads on iOS requirement (12.2 vs 17.0). ShiftRhythm's advantage is update cadence (every 2 days vs monthly). On price, review sentiment, ads and device support there is nothing between them.

Scored on Price · Rating · Positive reviews · Number of ratings · Update frequency · Ads · In-app purchases · Monetization · Best chart rank · Devices · Requires iOS

CostPrice · In-app purchases · Ads · Monetization

Both are free to download. ShiftRhythm sells 3 in-app purchases, starting at $2.99 per month. J asks for nothing beyond the download.

UpkeepUpdate frequency

J ships an update monthly, ShiftRhythm every 2 days. The most recent releases landed on October 10, 2026 and October 8, 2026 respectively.

Scorecard4 real differences · 6 level
J versus ShiftRhythm: the parameters behind the verdict, then further details
ParameterJShiftRhythm
PriceFreeFree
Rating5.0 (4 ratings) — better—
Positive reviews100.0% of reviews100.0% of reviews
Number of ratings4 — better—
Update frequencyMonthlyEvery 2 days — better
AdsNoNo
In-app purchasesNo — betterYes
MonetizationFree — betterFree with in-app purchases
DevicesiPhone, iPad, iPodiPhone, iPad, Apple Watch
Requires iOS12.2 — better17.0
Further details — not scored
Size19 MB16 MB
Age rating4+4+
DeveloperHeather MarriottJaeyoun Kim

Customer experience

J

All ratings4 ratings
Positive100.0%
Neutral0.0%
Negative0.0%
Written reviews1 reviews
Positive100.0%
Neutral0.0%
Negative0.0%

ShiftRhythm

Written reviews2 reviews
Positive100.0%
Neutral0.0%
Negative0.0%

In-app purchases

None

J

No in-app purchases

3 purchases

ShiftRhythm

Subscriptions2
  • Monthly$2.991 Month
  • Yearly$14.991 Year
One-time1
  • Lifetime$39.99

Questions

Is J free?
J is free to download, with no in-app purchases.
Is ShiftRhythm free?
ShiftRhythm is free to download, with in-app purchases available.
Do J or ShiftRhythm have ads?
Neither J nor ShiftRhythm shows ads.
Which is updated more often, J or ShiftRhythm?
J ships an update monthly, and ShiftRhythm every 2 days. Most recently, J was updated on October 10, 2026 and ShiftRhythm on October 8, 2026.

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