I have the Dual-stars, and have been happy with them except my switch just recently went bad and we have to replace it. I haven't had issues with uneven heating that Triple J mentions. I got aftermarket grips from Dual-star.
I'm ok with the high-off-low switch. We live in the SF bay area and the coldest weather I get is in the 30's. High is good for any speed when the weather is in the 30's-40's or for the freeway when it is in the 50's; low is good for lower speeds in the 50's.
As He Man says, they are not sufficient, they won't warm the fingers, but they are certainly better than nothing and it's nice to have a warming solution that is always there (in case the weather suddenly changes). I have poor circulation to my extremities (as do many women) and these temps cause me severe pain in my hands without the grips, even if I have a heated jacket liner on.
I would love to have heated gloves but haven't found any that are small enough for me.
The only issue you may have given that your girlfriend has smaller hands is that the Oxfords are of a larger diameter than the stock grips. I preferred this for myself and have no problem with them. She may not be comfortable with them.
Sorry to say, but this probably will be an issue. I know I wouldn't be comfortable with larger grips.