My understanding is the the FI works well but with more power. So you spend double the money for the driver and require double the power over the Alpine. For the same costs you could build 2 LilWreckers. If I had the space and budget, I'd build two of the LilWreckers with plenty of power for the FIs.
Also, don't cheap out on the lumber. I thought about it. LilMike talked me out of it. Shop around, look, and you will find decent lumber. If you are going to go to all of the work to build one of these things, why buy shizzy lumber? Too many people would then come back and blame the design rather than their poor choices.