a buff off is generaly a hard gel, and whn it is filed will turn to dust, a soak off gel has a more rubbery feel to it, I would say though, if you are buying gel products it is much beter to but via proffesional distributers, you just don't know what you are getting from ebay, and some products are actually dangerous. Buying from reputable companies means you have their customer service, and can call them to discuss issues and troubleshoot, also you would know exactly what you were getting as well.
A lot of people have tried ebay products, and most dont ever again as it just doesn last well enough, or causes damage at the worst, why not do a search here under best gel?? and then have a look at the top rated ones???
hth x