Grips are funny in terms of personal preference. Some folks think mag grips are like having a golf ball in your hand, for some folks (me) it feels like that center hump/bump nestles right into that center concave of the palm... the part of my palm where the thumb extends down is kinda meaty. I was skeptical of the TazRat but it actually fits in the hand REALLY well. The original Ratweiler works best for my grip but the small Basic grips always felt like crap to me - I know I'm in the minority. The full size original Basics weren't bad but the Rat/Dog/New-Basic res-c grips are great.
I would suggest that to find out if the Rodent 9 grip works for you, you've almost got to feel it. (I hate the standard Glock double-stack 45 grip like the G30.)
Based on looking at the pictures, the R9 would certainly have a meatier chop to it but I'm not going to suggest that it would necessarily outperform the SAR8 if it has a keen convex.
What's all that mean? Heck, just rambling but still trying to make the point that what works for one person, doesn't work for the other. Use the comparison pics to get an idea of size but approach grip compatibility skeptically until you feel a particular blade yourself.
Solution? Buy both and resell the R9 if it doesn't work for you.

I've done that with many, many blades. So much so that I used to have trade fodder but now mostly the "keepers" are left. It takes a lot for a new blade to push one of the keepers out of their spot.