Yes, heated grips are definitely useful. I installed a set of KOSO AM111030 grips on my RX3. Currently $126 on Amazon, paid $116 at the time that I got my first set. Just ordered another set to install on the TT250.
The higher price is due to the fact that they feature an integrated heat controller in the left grip, so the install looks OEM clean, without a separate controller attached to the handlebars. You can see them here:
https://www.amazon.com/Koso-AM111030...&keywords=koso
They put out plenty of heat, with 5 levels to choose from, each color coded differently so you can tell at a glance what they are set on. They also have the low battery shut off feature. Combined with a set of Oxford Rain Seal Handlebar covers, I can ride rain or shine down into the 20's F, which is about my limit on the bikes in the winter. The covers alone let me ride down into the mid 30's F for about an hour with my summer gloves (Scorpion SG3's), but then I need a little heat.