I can't say much for Sencore since I have no experience with them. Their products are way way way overpriced and they only support products manufactured only as far back as 5 years.
B&K is great. Product support goes back to 1970 (the model 467 rejuvenator). The oldest model (and still the best, IMO) is the 467. The good models are 467, 470, 480, and 490. Be advised the 490 is made in two versions: the original 490 (which uses the common "CR-" series adapters) and the 490-B (the very latest model and uses the all new "CA-" series adapters).
As with any rejuvenator, you'll need the various "adapters" that plug onto the back of a particular picture tube to connect to the rejuvenator. On B&K units, 90% of arcade tubes use adapter # CR-23 (your Nintendo will use that one). Your Matsushita is an oddball tube though. I lost my notes on what adapter it uses, but it was either CR-30 or CR-25. Be sure the B&K model you bid on has the adapters you need to use with your tubes. At the very minimum you MUST have CR-23 to do most arcade color monitors.
To use a rejuvenator the monitor power must be unplugged and the tube MUST BE DISCHARGED or the rejuvenator will be DESTROYED!
Rejuvenators do still fetch some money on ebay. If you found a good model for $20 to $40 consider yourself very lucky indeed. New ones go for $2,000 and most used ones go for $300 to $700.
Edit:
After poking around a bit on the B&K website, I've discovered they have discontinued manufacturing all CRT rejuvenators back in May this year. However they still provide Service, parts, accessories, and manuals. Here's the setup/instruction manual:
http://bkprecision.com/www/NP_search_model10-TP.asp?lf=CRT+Tester+Charts