I have a 72" Buhler Farm King RFM that I used for a long time without an i-Match. Recently I bought one and had to order a special kit to make it i-Match compatible. However, the kit didn't completely solve the problem on the bottom two lift pins and I had to buy two replacement speeco pins without the shoulders. Together with either a sleeve or a set of bushings (converting it to cat3), it now works fine.
The Buhler unit has worked well for me and I bought it from my local Deere dealer when I got my 4600. They sell these instead of Frontier as they are considered to be a better performing unit. If your criteria is which mower is i-Match compatible, you can go with either. Good luck.
-Bob