If I was Microsizer and all oem bits I would be in intensive care on live support right now writting out my will! There is no way Microsizer can compete with RS on this. Its the 10,000pound gorilla. Even ToysR Us and Walmart would have fun.
Bet Microsizer wanted to get their line out early before RS hit. From old threads about mid year I herd. Either it took a while through FCC certification { very possibly } or just a lack of products from Tomy to ship.
RS is a major retailler. Even though their stores are small they are everwhere! Just to prove how much. Goto
www.radioshack.com and select "store location". Scroll down the pop up windows and realize each blue dot is a store. These are only the US one and not world wide.

From my house with in 4 miles there are 4 RS stores! And one less than a mile!
I did some stuff for them back in the early to mid 1980. They are nice people to deal with. Hum. If the old logic still works then whatever they are charging then 1/2 of that price is what they are paying for it.
The thing that puzzle me is who is supplying them? This is not a small order to fill. I can see Tomy since they have done deals with them in the past or is this from one of the OEM? RS is big enough to fight off any copy lawsuits but are smart enough not to get themseleve even close to that. I guess looking up the FCC number could give a clue but odds are it would point back to RS.
You can enter Zipzaps at there site and it take you to a spot under RC car but just dissapears. Also its not under seasonal items so these guys are hunting bear! May want a Microsizer just as a collectable item.