In my opinion there is not a great deal of difference in the Pro and RTR.
Pro has threaded collar on shocks - RTR has clips but you can buy collars, not expensive. Other than that the shocks are the same.
Pro has CVD center line shafts - RTR has dogbones. The CVDs can be bought for about $24 each. Now this can be expensive but dogbones work fine.
Motor mount on Pro is lower to allow for starter box use. RTR doesn't need starter box because it uses a rotostart type setup.
Other than that the buggies are the same. With RTR you also get a nice radio. The motor is very nice for a .26 but is not race legal at some tracks. My tracks don't mind the .26.
Have fun either way.
Rockman