Our GS61 and BS63 double-padded guitar straps have been well-received for about 3 years now. We've had some good customer feedback in that time, which I always listen to. I also read the guitar forums to get the grass roots opinions on guitar straps.
There's no right answer. Some people like the underside to be slippy & smooth, some like grippy suede. So now we're using NUBUCK, a tough polished suede that's both pretty smooth and a little bit grippy too. Trust me, it works well for both. In fact, I think it's better than either smooth or suede - what everybody needs is a bit of both, and we're all happy.
(Nubuck is now also fitted on the Pinegrove BS64 4" wide bass strap)
I've also just been looking at how people attach their strap to their guitar, particularly at how many people like to wear them, to me, the WRONG WAY ROUND.
But hey, is there a right and a wrong way? Of course not! If you guys want to have the tail strap (the narrow piece) at the front then go for it. But I thought we could make the straps look better when that way round. So we've reshaped the rear end of the strap so it now looks super-cool when worn at the front. See that little taper, how it narrows slightly? I've just given it a subtle re-modelling without weakening the strap, and now it looks way way better.
Joe Supple at Guitar Magazine suggested we added the Pinegrove device to our straps. Great idea, but not too bold. We know that many people don't like loud branding.
More details are in the Double Padded Straps section at the top of the Guitar page. Click https://www.pinegroveleather.com/pages/guitar