The majority of those products are using foam as the absorption material. Unfortunately for the budget studio world, this stuff is widely used. It is not as effective over a broad range as rigid fiberglass or the Bonded Logic type recycled denim material. I have NEVER set foot in a real, professional level studio that uses much of the foam. They build false walls using many layers of rigid fiberglass combined with various styles of diffusion.
The Sonolites you picked will be a little better than average because they are 3" thick, so they remain effective to a lower frequency, but still not that great.
Check here for lots of options that are more affordable than typical hi-fi manufacturers:
http://www.acoustimac.com/They offer many options and even materials to DIY including the denim which is more money but much nicer to work with compared to fiberglass. The fit and finish of the lower priced panels is not the greatest, but just fine for most peoples rooms.
Also check out GIK, one of the site sponsors. Their products are nice, legitimately do what they claim and are still fair prices:
http://www.gikacoustics.com/Greg
