Wrist vs chest strap HRM

I use something different, optical up my arm in a fleshy bit.

Chest straps are superior in almost every way to wrist. Chest straps are much more accurate. Chest straps battery last longer (years Vs days). But some people find them uncomfortable.

My wrist based tracker (Garmin Vivoactive 3) seems to measure my heart rate plausibly during daily life and some types of exercise, based on comparison with years of past experience with a chest belt HRM (basic Polar model) and doctor's office readings. Recent research/reviews suggests the better quality current wrist-based HRM read HR pretty accurately for most people, though skin color or arm hair, among other things, can affect accuracy.

For rowing (water and machine), I add a chest belt that pairs with it, because the nature of the arm movement during rowing makes it lose contact and give clearly false results.

It seems to be plausible for pace/speed/distance measurements based on its GPS, as compared with years of experience with a previous GPS device (Garmin Forerunner 205) and map-based estimates.

Its daily step counts seem plausible, but I have no cross-check (and don't care very much - not much a walker).

Its counts of stairs flights are wildly inaccurate (again, don't care).

Its sleep tracker is hilariously inaccurate (and research suggests these devices are pretty bad at that in general).

I don't expect the calorie estimates to be accurate, necessarily: It doesn't measure calories, it estimates them.

Essentially, they use the same demographic research as MFP or TDEE calculators do, then make further estimates based on arm movements, GPS and altimeter readings when the device has those, plus heart rate (which doesn't correlate exactly with exercise).

They come close on all-day or exercise calories for quite a few people, those who fall near the averages from the underlying research. They can be off for some people (high or low), and fairly far off for a few.

Mine estimates a few hundred calories daily on the low side for me, compared with a year of carefully logged experience during weight loss (food scale and all that) and 3 years of maintenance since. It's off by about the same percentage for me as is MFP and most TDEE calculators.

As far as comfort: I'm old (63) and have always worn a wrist watch (most recently a sports watch that was chunkier than this tracker), so I don't even notice the wrist-based device. It's very comfortable. I've worn a chest belt during exercise for around a decade, so used to that, too. I wouldn't enjoy wearing the chest belt all day, though: For me, it would get itchy. Fine for an hour or few, though. Some women find they interfere with bra-band in a way that hinders accuracy, comfort or both. (Post bilateral mastectomies, I don't wear a bra, so don't know.)

So, depending on what you want/expect, it could be a good purchase. I wanted sound heart rate and speed/pace data for rowing and other activities, and it's great for that. I use its exercise calorie estimates for most intentional exercise, figuring that (a) it's close enough for most things, and (b) I know that consistent estimates are more important than strictly accurate ones, as I also monitor and adjust calorie intake based on scale weight.

I do use the MFP database estimates for strength training, though: HRM tend to be truly terrible at estimating that.

I find that the Garmin OHR's are pretty close for me. I have A/B'd them many times with Garmin, Polar, and Suunto chest straps for running, power walking, and intervals. They are almost always within a few BPM of the chest strap, and average HR is normally withing 1 BPM (if not exactly) of the chest strap.

But...

There are several factors that can make them not work well.

skin color
tattoos
hair
arm swing

Also, if not worn snug enough. If you jiggle your arm, the device should not jiggle at all. If it does, it could cause spikes, drop outs, and/or cadence lock.

For gym based stuff like weights, or anything that requires a lot of arm flexion, I would use a chest strap or a separate OHR that goes on the fleshier part of the arm.

As a female the type of top you are wearing will be a factor. Chest straps shouldn't be worn with sports bras containing underwire.

Chest strap is superior. my FitBit Charge 2 has wrist based monitor and it's ok for daily type of stuff, but tends to go a little wonky with actual exercise...I when I sweat it can drop off altogether.