This is not my review, just a round-up of reviews on Sanwa trackballs on many Japanese websites.
There may be a few members in this forum who are interested in them so for that.
Bottom line: I guess that most of them don't even worth a review, though there may be exceptions.
This one seems to be an OEM product of "Libra 90 Trackball".
It's pretty old model and now it's the only Sanwa trackball which does not use the optical sensor.
I know there's some people using this and satisfied with it, but they also say that its molding is very crude and it's useless without modification and maintenance.
With some modification it may turn into an excellent, yet inexpensive 50mm trackball but I don't really know.
Sanwa "Stingray" MA-TB30UPS -
Most people consider this as a much inferior imitation of Microsoft Trackball Optical or Logitech Trackman Wheel.
Sanwa "Stream" MA-TB32UPS -
Looks good in appearance, but it actually is widely known as an absolute failure, thanks to the poorly positioned optical sensor which makes proper control of the pointer virtually impossible. In addition it has a number of weaknesses as well.
Sanwa "Stream R" MA-TBW34S / MA-TBW34B -
Wireless versions of MA-TB32UPS in two colors (silver and black).
Seeing MA-TB32UPS, very few were brave enough to try this out, so not much information available.
Sanwa "Force" MA-TB35DS -
Many say its scroll wheel is weak and not very useful.
If you want a "bigger" trackball in a limited budget in Japan, and you can live with just two buttons
and a not-so-reliable wheel, this one might not be totally worthless.
One good thing is that the ball is the same as the one in Trackball Explorer in diameter (46mm).
Sanwa "Opt-trackball Pro" MA-TB38S / MA-TB38BK -
The latest trackball (Dec 2008) by Sanwa Supply is rumored to be an unbelievably good product, for Sanwa.
Actually, it is mostly considered as a cheaper substitute for Kensington Expert Mouse, but its price (half as Kensington EM7) is enough to justify its quality - maybe.
This is a brand-new product and the reputation is not really fixed yet.
Sanwa Supply official site (in Japanese)http://www.sanwa.co.jp/http://www.sanwa.co.jp/product/peripheral/trackball/index.html