Suffice to say that the ones from wemoto were rather expensive, so I decided to buy some cheaper ones off ebay (https://www.ebay.co.uk/itm/402546184918). They look like this:
So, they look kind of plasticy, but that'll be ok... right?
Well, on closer inspection (once I'd got them on the bike!) I realised that they actually have 10W bulbs in them rather than 21W bulbs like the originals!
I probably wouldn't care about this, however the difference in resistance between the 21W and 10W bulbs cause the stock flasher relay to go haywire, so I had to 'upgrade' my flasher relay to an LED one that doesn't care about the load (despite these not being LEDs).
In addition to that the thread is a smaller size (not the same diameter as the original ones) and I think they'll fall apart in about 2 weeks, but I was kind of expecting problems like that so I wasn't surprised ;)
The thing you should bear in mind is that these not-so-great indicators were marketed on ebay as 'Indicators Set For Honda CB 500 S Twin 499cc 1998 - 2002'.... hmmm.
Have fun out there, it's a jungle.