it seems they have something to hide. They want people to sign up first. I always avoid these spam like web sites. The whole world and his dog just don't need my email address for no good reason. But if you like it cool
I say just get yourself Photoshop, get familiar with it real quick through YouTube tutorials, it's easier than ever and really quite intuitive. It seems to have become an absolute requirement for YouTubers nowadays, and most of them barely know the very basics and fundamentals of the program.
GIMP is the best alternative to photoshop that I have found, it has almost all the same features, and can actually do things that Photoshop hasn't implemented yet. I use Photoshop personally, but GIMP is a great alternative! It is free, and there are tons of tutorials online on how to use it!