It looks like everything they sell except for their 4" kit is a budget boost (spacer lift). Spacers are pretty much spacers, but there is a wide difference in shocks, and I'm not familiar with their shocks.
The 4" kit doesn't look like it has anything to address drive line angles/vibrations, and it has the normal fixed lower control arms that are inferior to your stock arms.
If you're interested in a BB lift, I recommend you just buy spacers, then select some quality shocks. If you're intersted in 4" of lift, check out the Zone 4.25" combo lift for around the same $'s. Zone Offroad 4-1/4" Combo System 97-06 Jeep Wrangler TJ J25/J26