Hi:
...the price difference is due to the size of the unit ordered. The super large one is about $600, the super small one about $100.
Keep in mind that there are dozens, if not hundreds, of these things that LOOK identical from the outside. That doesn't mean that they use the proper power output, or that they are made with quality materials, especially since we're talking "made in China".
I think we got extremely lucky finding this source (we researched for close to two months), as it seems the quality is actual medical grade.
Joov is the gold standard (and based on pricing, I"m assuming they are made of gold LOL) to compare with. $1195.00 for the same panel configuration as we have, with power output almost identical.
The difference is that our unit is the "old" analog technology, the new Joov units are digital. However, this doesn't impact how the units actually function!