I used a FitBit for about a year some years ago. Basically, it did little for me except provide some info on sleep patterns. But FitBits were very unreliable at that time, maybe still are if they even still exist. Had more than one warranty replacement.
A few months back I tried a continuous glucose monitor just out of curiosity for two weeks. I’m not diabetic so it just showed expected things like a spike after eating that would settle to baseline in 30 minutes or so.
I thought I might see something interesting during rides, but basically my body just did what it was supposed to do and levels stayed pretty normal. I’m sure if I didn’t fuel on a long ride and bonked, it would have shown that, but I wasn’t going to intentionally bonk just to see what happened.
I use a Garmin bike computer religiously, and really enjoy the numbers and playing with data. I don’t train but do target miles and hours per week, as well as have some power goals on most rides. But sometimes these goals are to hold the power below a certain level. Not always to push to some target.
I get how some people like data, like me, and some couldn’t care less about data. Different strokes for different folks. I think this can also explain why some people only use these devices for a short time. They simply have to try them to find out if there is anything of use to them. They find out there isn’t, and stop using them.
I do see how for some it might be a bit like weighing yourself daily and getting discouraged with what you see. Especially if you place a lot of expectations on the numbers.
I have done more formal training, the data showed it helped, but the work I put in was not worth the results since I wasn’t competing and the relatively small improvement wasn’t worth it to me. I also learned how quickly fitness gains, that took months to achieve, are lost when illness or injury keeps you off the bike.
My point is the data didn’t discourage me, it just gave me the info to decide that training hard wasn’t worth it to me.