+1. I have dual hole spirits on a few unis. Only once have I bothered changing crank position during a ride (short to ride to the trails, longer on the trails). Usually I’ll “suffer” the longer position on the ride to the trails. With QR pedals I could see myself doing this regularly.
I got a couple of samples of Wellgo Quick Release pedals in the mail last week, with pedal body no. QRD-5219. Unlike most of the other QR hub bodies I’ve seen, this one seems pretty good.
I wanted to check if it was possible to install two quick-release mechanism at the same time, in a Spirit double hole crank, without any modifications. Unfortunately I received one right and one left pedal only, so could not install both on one crank to physically check. The below is based on measurements.
As many of you know there are two QR mechanism types that screw into the crank: one with a button, and one without. See the attached photos. The “button” style requires about 5.5 mm space on the side of the pedal hole when installed, but much more to screw it in. So there is no room between the pedal holes to screw two QR mechanisms of this type in at the same time.
The “circle style” requires about 8.75 mm space on the side of the pedal hole. It has no button but due to the thicker body you cannot screw two in at the same time.
If you combine both styles, the two require at least 14.25 mm room between the pedal holes. That means that both should fit on the 110/137 and 137/165 Spirit cranks, but not on the others.
So for the 110/137 and 137/165 lengths it likely works; for the others I don’t think it will work, unfortunately.
I can’t provide an opinion on the strength or durability of the pedals because I haven’t tried them. Based on visual inspection, the QR mechanism looks like it will be good for general road or possibly XC Muni use, but not strong enough for drops or aggressive riding. Personally I’d see these as most useful if you frequently take pedals off for storage or transportation.
I’ll leave them on my muni for a while to see how they test out.
Attached are closeups of the two styles on a geared KH24.
Kris
So you’d have to but two pair in order to have both crank holes fitted with the receiving end? Or do they sell those separately?
Unless UDC started carrying them and splitting the pedals, at the moment I don’t know how you’d get around buying two pairs of pedals, as far as I know.
I can see the convenience of being able to make a quick change, but as you mentioned, they probably wouldn’t be ideal for any kind of extreme riding. At present the only uni I make regular crank hole changes on is my KH 29er that I modified to a 700c for road climbing.
I use a thin, lightweight 15mm bike “cone” wrench and it takes only a minute or so to switch both sides. But I’m usually in no hurry since I only make the change after climbing several miles, so after a short break I switch to the shorter holes for the ride back down. 
Attached are a couple of photos courtesy of UDC Australia, showing MKS quick release pedal inserts in a pair of 127/150 Spirit Cranks.
Note that the pedal body in the photo won’t work as they will hit the other insert, but MKS seems to have other options that might:
http://www.mkspedal.com/English/catalog.htm
Hey Kris, I’ve seen pics where someone was able to use side by side inserts, but they had to cut back the cage to clear the second insert.
The biggest problem I see is that the pedal is set out further from the crank, so it’ll increase the stance by a 30-40mm.
Did you take a look at the White Brothers QR crank??
That’d be a cool option for Spirits or a neat remodel for Moments.
Personally, I don’t swap cranks more than once in a blue moon, though most of my unis have two holes.
I’d be more likely to use a second hole if they were closer together in length, so 125/137, 137/150, 150/165. Yeah, I realize it’s not physically possible for two holes to be that close “the way the cranks are designed now”, but it could be done if the design were diffent…
I’m mostly satisfied with one crank length, 150’s seem to be good for all my big wheel application, 137 or 125 for small wheels.
We wouldn’t have to worry about silly things like crank length if we had more gears…
I see QR pedals as potentially useful for riders who use public transportation a lot and have rules & restrictions (or practical limitations) on getting onto crowded trains buses & subways. I also see them as useful for riders who regularly pack many of unicycles into their vehicle on the way to, say, a club ride.
As far as double hole cranks go, I think they are really helpful for riders who have only one, single speed muni (e.g. almost everyone except many on this forum) and use it around town during the week and offroad on the weekends. Even if you don’t use the second hole it’s a good way to slightly lighten the cranks as long as it’s carefully considered in the cranks design. I don’t think many riders change crank length halfway through a ride, but it is helpful if you commute by road to a trailhead, and then home again after the ride.
As far as crank lengths go, I could change the 110/137 to 117/137, potentially.
Kris
I recently tried a setup as discussed above using the MKS Ezy pedals ( Lambda and clipless). I did a detailed write-up here with some pics and discussion of pros/cons.
http://www.unicyclist.com/forums/showthread.php?p=1686161#post1686161
I linked this thread in my post.
Cheers