If you are a drummer then until you get up over $2,000 there's no huge improvement in "realism" of the sounds generated either with the brain or triggered samples. But there will be a more musical (real) performance recorded. With the basic kits ,they are about the same thing as an octapad, something to hit that bounces back, But the big difference is that you can play it like a kit with all 4 limbs. So if you are
not a drummer, stick with an Octapad type trigger.
I bought the Yamaha DTX 400 as it was the best buy of the starter kits @ $500.
The sound in the brain are actually very good, They are almost identical the the Birch kit found in Session drummer. I also find the sounds respond better to how hard you play than triggering samples, but I still use Session drummer for my drums.
I had a chance to play the flagship Roland kit, wow, now that is real, Every little nuance is captured and the skins are very nice to play. But It was $5,000.
But if you can play a full kit of drums, having even a basic kit to whack on will speed up the process of laying down a better drum track. I used to enter my drums on a keyboard in a few passes, Kick, then snare etc. Now I do it all at once and the accents and fills make musical sense. So the performance is much improved as you can play the part more accurately than with you fingers.
To get true sonic realism will cost you a lot more.