I had used a Boss "expression pedal" as a volume pedal for many years with my 6 string prior to starting pedal steel.

In order of acquisition (left to right):
Carter Starter VP
String type VP that came with the Starter Kit. Action is good. Has I/O on the right side and two unused holes on the left that could be made into extra outputs. Pot was scratchy almost from day one. Contact cleaner clears the problem up temporarily, but the noise relegated this pedal to backup status pretty darn quick.
Ernie Ball VP junior
String type with jacks on the end. A little taller. Has a PF tuner out. A "guitar" pedal, so wrong pot impedance for PSG. Well made, but my string broke after a couple of months use. String is PITA to change IMHO. Has a small slider switch to choose between two tapers. Nice.
Dunlop DVP1
Jacks on the end with tuner out. The tallest of the bunch. Build like a tank. Great feel. Adjustable tension. Another "guitar" pot pedal, but with unique steel band linkage instead of of string. Supposed to be more durable, but I have broken two bands with less than 16 months use. Dulop has been great about fixing them under warranty, but I wouldn't trust this pedal without a backup on a gig.
Morley VP Junior
Jacks on the right. No tuner out. Another "guitar" pedal. Uses a pair of LEDs/Light Depedent Resistors to emulate a potentiometer. So it's an optical pedal, but not an "active" pedal in terms of signal flow. I bought this as an emergency backup while the Dunlop was being fixed. 9V batt or DC in. Only problem IMHO is the taper. All the gain is at the bottom on the travel. I have recently learned this can be tweaked in a number of ways, so I'll be doing that now that I have an "extra" VP
Hilton Pro Guitar
Wow. Should have got this a long time ago. The Pro guitar model runs on 9V (instead of 24v) and has adjustable tension (which I have not tried). I just got this last week so cannot say about durability, but seems very well made. 1 gig using it so far. I used to always use a compressor between the PSG and VP, but as soon as I started using this pedal, the compressor stays switched off mostly. That says a lot.
For all of these; I didn't mention "tone", arguably the most subjective aspect. In my 45+ years of pro/semi-pro 6-string playing, I have come to believe that tone is 90% in the fingers. Sure you can kill good tone with bad gear, but right now my PSG picking produces mediocre tone at best most of the time. I'm still mastering metal finger picks, so the subtle tone differences in volume pedals is relatively small for me. Having said that; The Hilton pedal, being active, does have the same tone at any volume compared to the passive pedals which do not.



