Thanks for the info, guys. I'm glad I asked, instead of just assuming the Happs would be better and going with that. Now I just have to see how long it will be before GGG has their's back in stock. I emailed them this morning - haven't heard back yet.
As for what games I'll be using it for, primarily stick + spinner games (Tron, Mad Planets, etc.) Also for the two stick games that need a fire button, like Battlezone and Assault. The two stick games are going to be a little awkward, since my two main sticks (already purchased) are T-Stik Plusses that will be front and center with the button-top above and to the right. I'll have to use the button-top in my right hand and the Player 2 T-Stik in my left hand, so my hands will be cockeyed relative to each other, but I think it'll work okay.
If I like the GGG button-top and if I ever build another cab, I may just go with two button-tops as the main sticks, and a dedicated 4-way as the third stick.