Looks like an improved version of the Best Products one (http://www.walmart.com/ip/29608014), with heavier-duty construction, vastly improved ankle clamps, and a memory foam board. And twice the price. For an extra $35, you can get the Woot one with a contoured bed, pillow, higher clearance (it seems), and acupressure points.
http://bestinversiontables.org has reviews of both, and rates the one here a half-star better.
http://bestinversiontablereviewsx.com rates the Ironman one better, but doesn’t say why. Both sites seem to make their money off referral sales.
http://www.inversiontableexpert.com/comparison-chart rates them the same.
http://inversiontherapyhq.com/inversion-table-reviews-5-things-look seems to consider them equivalent, just different.
Finally, http://inversiontableanalysis.com ranks the Woot item as the best table, being more comfortable and having stretch grips. This is followed by an article on the Ironman Gravity 4000, which notes a lot of positives, that it costs less (remember, there’s normally a bigger price difference), that it’s easier to assemble, but harder to store.