I have an Alesis SR-16 and have tried the cheaper Zoom machines you have listed. The Zooms did not have a midi out, meaning you could not record to a seqeuncer, or trigger other sound modules. The sounds in the Zoom machines are better IMHO than those in the SR-16. For the most part, SR-16 samples sound like 80s drums with too much reverb, but i have managed to build a decent dry kit. The SR-16 also allows the user to tune each drum, and to route the drum through different outputs. there are 4 analog outputs on the SR-16. The user could put a snare drum on one channel and the kick drum on another channel for different compression effects etc.
Even with all these handy features, I still think better drum sounds can be had by using a software sampler.
i use my drum machine to write patterns and for practice and to lay down quick tracks in a song.
Steve