I've just fitted them to my windows and they work fine. I used them because two jaws had fallen off (one of them was missing). If you're replacing the felts along the top of the metal part of the door too, you won't have to notch them to clear the jaws (one of the benefits). The downside to these new channels is the price. Bud's sent them UPS to me here in the UK and it was $89 on top of the price of the parts! To add insult to injury I had to pay customs charges of another £24 (yes, pounds) when they arrived. I rang Bud's and complained that they'd obviously made a mistake but they were adamant that the price was right. If you buy them, try to get US Postal. Takes a bit longer but much cheaper. I've bought a few parts from the USA recently and sellers like the traceability of UPS parcels. I'd rather wait a few more days than pay those kind of prices. Rip off if you ask me.
Anyway, the bits I got from Bud's are metal with a material and felt-like covering. Their construction seems very durable. No idea where you'd get something similar over here.
Be careful when removing the old jaws. I took out the retaining screws and soaked the jaws in penetrating oil overnight so they were easier to remove.
Mark
Billericay, Essex, UK
Late 67 LHD 250SL