My biggest concern was the 25 key limit. As I'm working on a budget, I couldn't afford the 49 key, and the 61 would be too big for my desk. It was either the V49 or VI25 for me. I am SO glad I went with the VI series. If you're wondering if 25 keys is enough, ask yourself this question: what am I going to be playing? If you're just using it to put in simple chords into your DAW, this'll work great. As I already mentioned, soloing is what this thing is designed for. I've included a short video demonstrating a solo that requires the use of multiple octaves, to give you a good impression what it'll look and feel like switching between them. Sorry in advance for the quality, I was using my webcam as the camera and mic.
As for the drum pad, the buttons are very sensitive. Good detection, and it's cool that you can trigger them just by pressing, not striking. This is where my only "con" is. If you're getting into your music while using the pitch and/or mod wheel, it's quite easy to trigger the pads and screw up your sound. I hope there is a setting within the Alesis software that I'm unaware of that will fix this. If not, it'll be something I just get used to. Either way, not really a con, just a heads up.
The nobs and buttons can all be mapped to various functions within your favorite DAW. I'm using Mixcraft 7 Pro Studios and everything seems to work wonderfully. That is, after I configured the play, stop, loop, etc. buttons.
Aftertouch is an amazing feature. For those who don't know, aftertouch is the ability to press into key after it's been struck and at it's lowest point. This can trigger different effects to your favorite synths. Think of it like 3D Touch for your keyboard. It's cool, but I haven't used it much.
I am VERY pleased with this product and am glad I bought it. If you're on the fence and have the money, get it.
**Update**
After using this product for over two years, my only issue is the USB port. As I was playing, if the cable was moved slightly, it'd stop sending midi data to my DAW. At first I thought (and hoped) it was a bad cable, but I was wrong. I put up with it for a while, but it seemed to get worse. I was about ready to purchase a new, different controller. As a last resort, I took it apart to look for any problems. After examining the port, I found three out of the six solder points were separated very slightly. After a few minutes of soldering and hot gluing, I finally have it back to it's original functionality.
While I still love this controller, this issue reflects poorly on the build quality and longevity of this product. If you're not a geek like me, you'd be spending $100+ on a new controller.
Without a doubt this thing is great for the money, but don't expect it to last forever. :)