I've got a PUK 3+, and am quite fond of it.
I did a review of it when I first got it, you can find it here:
I keep meaning to update that review, but haven't found the time.
Short form on the updates: you can't get the aux shutter any more
(not that you would have wanted it in the first place) and I loved
mine so much I eventually bought their microscope to replace it.
VAST improvement. Silver is possible, but a PITA with a 3. (I use
mine mostly for reactives, and am very happy with it for that use.)
I've chatted with the Lampert tech guys (from Germany) at a couple
of shows, and apparently the difference between the 3+ (mine) and
the 3S was that they broke the hi-freq start out from the high power
mode on the 3S. You want Hi-Freq start for silver, so having it
loose from the high power mode is a good thing. Don't know for sure
what the further differences are between the 3S and the current 4.
What I can tell you is that the Lampert guys are very good with tech
support. If you have a problem, they really will go out of their way
to help you. They even custom built a power unit so that I could add
a 'current' model microscope with LED lights onto my 3+ when I
finally broke down and bought the scope that I should have gotten in
the first place.
OTOH, I have worked a booth with Scott, the Orion guy, and he's good
people too. Didn't get much time to play with the Orion, but it does
have the handy 'sparky' mode, for doing fusion findings, which could
be most handy, depending on what you do. It does have a touch
screen, and appears to have a bit more on the display,
certainly than the PUK 3. I think one of the changes with the PUK 4
was that they added a better display, so that could be a wash.
Actually, I just looked at the specs on the PUK 4: it looks like
they've added a touch screen, and the ability to 'spark' fusion
findings, so the two machines are pretty well matched there.
The build quality on both of them is very good. I've held both of
them in my hands, and owned one. Yes, they're expensive, but they're
built like it.
For whatever that's worth.