For those of you that have or had large tools on mobile bases, where you happy with the way they worked or did you feel they were more stabile off the base?

I have my 10" bandsaw (admitedly not a "large tool" by most standards)
on an HTC mobile base model #HTC2000. I've been very happy with it -
seems just as stable when locked as without the base. I also made my
own base for my DP - basically got a rolling tool cabinet, pulled off
the cheapo casters, bolted on 2x4 'outrigger' legs, and put good
casters on the outrigger-ed legs. See below for caster description.
These locking casters are fine for the DP where there isn't much
lateral force.
Roy, I suggest you take a look at these casters on ebay - item number
7559591283. They look a lot like the ones you linked to at Woodcraft,
except they're on a bolt instead of a plate. I ordered a set to make
my own DP base, and they work very well. Both rotation and swivel
lock.
In summary, I'm happy with a commercial base and my own version in
their current uses. They're both functional. I don't think I'd want
to rely on the locking casters alone to hold a TS or jointer or even a
router table steady in use, but it'd be easy enough to put on threaded
leveler feet to extend past the casters "lock" the base to the ground.
Hope this helps,
Andy