I am working (booo) so I will be brief.
I have the practice pad, first version. It is great for a quick blast on with a cup of tea after work....untill I upgraded to a full kit.
The practice pad is good for rudiments, learning, general stuff. It has an interesting function where you follow the click, then it drops out, see how far out you are!
It also has accuracy recording etc.
Now, from an electronic Kit point of view I hummed and harr'd and ended up saving a little longer to get mesh heads (apart from kick). This was essential I found. I bought a Roland TD6. The Brain actually gets little use from me, I midi it straight to PC. But I find the whole higher grade rack and mesh pads muct more friendly when jumping from a real kit to an electronic one. It is good to be able to move the hats, snare etc to suit what you are doing.
It will never be perfect, but I find I get a lot of practice in now that I would have never done before. Taking sloppy parts from band practice and working on them, and writing new parts for new tracks.
Hmm they way I talk I should be a drum god by now!
in truth, probably about 3-5hours a week on the Roland
It is a lot of money, but to be honest if you know you will be getting a lot of play time on the thing it will be worth it!
Whack it into addictive drums or BFD or something similar and you have an already decent sounding midi controlled recording feature at your finger tips!
I hope this is of some help.
Oh, and to answer your final question: Yes I think with the time put in to practice of course your playing will improve. Be it rudiments, full kit, playing along to CDs from totally different genres. Any time put into the thing you enjoy will be rewarding both for you and your playing.
my fav at the moment is putting on bassdrive.com and playing away (once a week
), sounds naff and far from live D&B, but every time i get a little faster and find something else I can do