Yes it does require usb host control but a lot of phones now have that, and like Bob mentioned the cable is quite cheap, I think around $3 or so on Amazon. What I like about using the tablet is the large screen and you can also have it autofocus by touching on an area on the screen. The focus stacking is quite good. I have tried the Helicon app and the Dslr Controller app has more features and is a lot less money. Being kind of a gear junkie, I have the tablet, promote control, and timelapse+. The promote is the best for portability and price and for the flexibility I do not think is overpriced, at least in my engineering experience. Their customer service is also excellent. On mine they battery leaked and destroyed the cable and board inside, they replaced it free of charge and overnighted me a replacement because I was leaving on a trip. In terms of time saving and what it can to, it is not as expensive as some of the bags, and certainly less than ballheads and tripods and other gear we use every day. Doing things in remote locations like doing focus stacked panoramas, or hdr panoramas make the promote worth the cost.
The amount of money most of use spend on photo gear is huge and the cost of a promote is really not a big expense in reality......
Just some thoughts from a curmudgeon in the morning... :-)