Sorry to hear that, Richie. I don't allow the diodes to be exposed to the air for more time than is necessary. I have yet to lose one of the Mitsubishi's.
638 nm is more visible, more popular than 650nm. I would buy 638nm one to see bright beam. 650nm is common, the cheapest color of laser pointer and just dim like 405nm.
If you want a powerful 638nm red laser I'd stick to the Mits ML501P73 as they hold up better than the others we've had. That diode can be pushed over 1 watt, but the Ushio, not so much.
Can't really say as the only two Ushio diodes I had both failed as I was trying for at least one watt. That was back when they first became available to us. The Mitsubishi is by far the better choice and I haven't really heard of anyone in quite sometime who bought one of those Ushio diodes. They have no advantage at all over the Mits.