Whoop seems to be hit or miss. Personally I’ve been using one 24/7 for 9 months and have not had any issues and it appears to me to perform the same as my Wahoo Tickr strap (a great strap BTW if you’re going that route). With the Whoop I’m getting 24 hrs of data per day, not just workout data. No drop outs, no spikes and nothing that appears abnormal in the in workout HR numbers. But, it appears some people do have issues with the Whoop. Any wrist strap HR is sensitive to how and where you wear it and while they work great for many (like me) they are generally regarded as having more potential for bad readings than a chest strap.
For me, the Whoop works fine for cycling. I don’t notice any anomalies and anyway my focus on the bike is power not HR. A big plus for Whoop is that since I have it on 24/7, I’m now capturing HR data from any other workouts (or play) I do without the hassle of putting on a chest strap. And the 4.0 will add more data. Finally a huge plus for Whoop over a chest strap is I get sleep tracking and automatic HRV readings. That’s become my main use of the Whoop.