I originally used Delrin W wheels running on the corners of 2020 misumi for the z axis of my corexy. I found that the run out was unacceptable even if the wheels were very tight there was a lot of slop perpendicular to the carriage. I ended up using vslot.
I tested them on 20mm t-slot corners. It works fine but I did find they made quite a bit of noise (more than LM8UU’s) so I ended up using them with Spectra line instead on my new machine.
@Wolfmanjm so, the run out was an artefact of the delrin being imperfectly round or not centrally aligned on the shaft?
@Richard_Horne hmm I hadn’t considered noise. Did you experiment with any lining materials?
+Thomas Sanladerer the -vv bearings make me nervous as a Spectra pulley. Some of the bearings I looked at had a square notch at the bottom of the v-groove that could chafe the line. Others had a round corner at the bottom of the groove. I didn’t find any way to be certain which type I would be getting. So I’m looking at using u-groove bearings. 624-uu appears to be plentiful and cheap.
Alright, I’m going to buy some on the basis they may well be useful as spectra idlers. I’ll get some UMWPE tape too - the old 3M anti-squeak stuff should do it.
@Tim_Rastall
no the runout was due to edges of 2020 not really being designed to be linear slides 
the delrin w wheels where perfectly round from grabbercars (when he sold them). If you were to have 4 wheels for each edge (so basically 8 per runner) it may be better, I tried 4 two on each side, but was still not very good.
@Tim_Rastall sorry for short and not really scientiffic answer, was late in my timeline and replying from phone.
So if you want propper replacement for bronze bushings, go for these http://www.permaglide.com/ks-permaglider/ks-permaglider-plain-bearing/ they wont wear out and they are perfect solution for ultimaker style gatrys. For sure much better solution than bronze bushings. We use them mainly for guidance for actuator aplications, best suited where not enough space to put normal bearing or lets say perfect for ulimaker style gantrys becaose of not only linear motion but also radial is applied to the mechanics. Please note, these are more expensive than LM8`s from china.
Now, if you really want to save money, dont use these V vheels on aluminium rail, it will just wear out (rail), like I said stuff happens. Problem is, you always want some preloading for clearence free motion and this preloading will do some damage at some point on the weaker material.
But, simmilar solution is made with roller bearings on aluminium profiles, only they use shafts (grounded, polished, hardened), so the rail is actually supported shaft. This is somewhat good solution, but again if you want precision, its not proper way to do it.
Generaly, roller bearing carriages are used in conveyor applications where high speed is used (im talking more than 1m/sec) and precision wanted is within 0.3mm or even greater, but for linear motion its for sure better to go with linear rail. It will only cost you at the beggining, but in the long run it will be cheaper for sure.
That said I really dont like V-slot, makerslide and all ot this solution, becaose none of them is good on the long run and not being soooo much cheaper than linear rails, especially if you calculate the cost&hastle of maintanence over longer period of time. Iam in the “motion” bussiness for 10 years, and I would understand that you want to save money back then when linear rail was more expensive than bar of gold, but prices went down hard since then and now really is no real point of taking short cuts that will bite you later on.
@Tim_Rastall No, didn’t try liners, it all started feeling too tight. I was aiming to make a tall high speed delta so stopped when the noise and it was getting much more complicated for no good reason.
@Tim_Rastall It’s good having a stock, I use them for spectra idlers and tentioners now. The 3mm ones are also very small.
You can also use them as a filament idler in an extruder - really helps to keep the filament guiding in a perfect straight line while you drive it.
I will use them on my Delta repstrap where they will run on chromed steel tube. I can already tell that they create an incredible amount of noise. I will probably put tape on the tubes to reduce the noise and print out new carriages with crossed roller bearings as replacement if they don’t work out.
I now got my printer up and running, the bearings seem to work ok and the noise is not at all as loud as I thought once the towers were bolted in place. Some of the bearings I discarded immediately since the cheap bearings I use are very uneven quality wise.