Might be boring but I went with the waffle strap from the SBDX017 MM300. Weirdly the same strap doesn't come with the new SLA021.
£55 plus shipping from the Netherlands on eBay so had to grit my teeth but perfect now and no bits of fluff all over the strap constantly.
I have a black isofrane on a SRP777 but didn't try on this as I don't think it'd suit.