Game develop actually was made a little after construct classic, before c2. The interface does look similar, but I don't think it's a ripoff. Mainly since it's author said he wasn't aware about construct when he first was making it.
I've tried it a time or two, but it didn't really capture my interest. I didn't find the interface to be as intuitive as construct's, and it seemed that the event system requires you to be more verbose. It does have some interesting features though.
You won't really get a lot of people saying they use it asking on this forum. Ask on their forum and you'll get a different response.