Up until recently, I had experience only with the heated gloves from Tourmaster (the Synergy line). I liked them as they connect nicely with their heated jacket liner (which I also have). The gloves are rated (according to them) at 24 watts (2.1 amps); the jacket liner is 76 watts (6.7 amps).
For new bikes, that (extra load) on the charging system is not much of an issue. For us others with the "wimpy" alternator, I was 'doing the math'! I was not confident in the charging system to installing high(er) amp heated grips and using an electric jacket liner. So the "wrap around" of heated winter gloves seems the choice.
For the gloves, 24 watts (total) means 12 watts per hand and (for me) is not a lot of heat, but is some heat. I find that if I keep my core (and my neck)warm with a heated jacket, it tends to push out the heat to the extremities (hands, feet, head).
Then I got an additional bike that had factory heated grips (and a huge charging system). I could not believe the amount heat that poured out of those grips! That, and a fairing that also shields my hands, I now give the gloves to my SO to wear. Hands are hot and no wires going between my jacket and hands! I like that. Heated grips are wonderful. And they are always there (like others pointed out).
If really cold, I will still wear my heated jacket liner. (or skip that too and turn on the heated seat...)