I took out a lifetime Gakuu membership last year around the same time the 80% off deal started. Fortunately the deal is still ongoing for those who haven’t taken out a lifetime membership there yet. I’m still going through TextFugu at the moment so won’t be using Gakuu just yet.
From what I have seen when I’ve logged on, it’s a nice site. It’s more geared towards advanced learners of Japanese. It’s similar to TF in some ways, but I think Michael (the owner) is still in the process of trying to make a textbook out of all the lessons. The forum isn’t that active but I have seen a few TF members post there. All the lessons are checked by native Japanese people too.
I reckon it’s worth taking out a lifetime membership as it’s so cheap, and the site will no doubt grow bigger like TF has. If it ends up not being for you, then you won’t feel that you’ve wasted too much money.