Tera's coil spring setup is NOT a cheap setup. I've been wheeling for a while now with guys who beat the PISS out of it every weekend, and less than 1/2" of settle, and no sag. Figure 3-3.5" on a 2-door, 3" solid on a 4-door. Great company, great customer service, and a lifetime warranty that's not on crap-in-a-box like Rough Country. I'll recommend their stuff (even though I run Rock Krawler) any day. Go to any OHV park and look under the JK's there- I bet at least 1/4 are running Tera. None of the guys on blues or harder will be running RC, at least, not that drive it home at the end of the day
Their shocks, despite the crap they peddle, are not a "unique design"- it's the same junk a lot of other guys use. Tera's shocks aren't great, so I'd recommend Bilstein 5100's, but at least their springs don't sag under a stock 2-door like RC.
As to the OP, the Budget Boost (spacer lift) is just a chunk of rubber (poly) that goes between the spring and the spring perch. It does nothing to help ride quality, handling, etc. It's just a chunk of rubber, and will act as such. A spring lift includes redesigned new springs- they lift via longer coils and different rates. This re-engineers the handling and ride quality of the vehicle somewhat to compensate for the taller height. This is why most serious folks go this route. It is more expensive, but can allow you to improve on the vehicle's dynamic abilities. The biggest thing to fix, however, is the poor dampers (shocks) on the JK's. Go with a set of premium (Bilstein 5100's are a huge success here, and I'm hearing good initial reports on the new OEM-replacement Fox shocks, although I don't think they're 100% available to the public yet) shocks, and really transform your ride.
Either one will fit 35's under it, but the coils will give you a bit more room for off-road flex, and won't degrade as much over time as spacers inevitably will- Mark W.