I am 6'3" with a 36in inside leg. The OnOne site suggests a 21" frame but I don't really want to be riding a 'farm gate'. Will the 19.5 build up ok with a 400mm seatpost? Or am I better off going for the larger frame? Any input will be appreciated.

Buy based on the TT length you want rather than the seat tube length.

But yes, you'd be fine with a 19.5" and a 400mm seatpost. I'm 5ft 11 with 33" inside leg, ride an 18" On One 29er and have a 410mm Thomson fitted. There's loads of seatpost left in the frame, so much so that I could have got away with a 16" should I have decided to…

I'm 6'3" but have shorter legs (and therefore longer body, I assume!) than you. 19.5" was spot on for me.

Might you be able to try one out for size somewhere. I've sold mine otherwise I'd offer.

Im 6'4" with 36" legs.

I used to ride a 21" scandal and liked it very much, but testicular clearance was limited on anything technical. When I bought their Ti2er I went for the 19.5" (although design differences mean its not apples with apple). Clearances were much better and I dont need a huge seatpost to maintain cockpit size.

They are a bit thin on the ground hereabouts. In fact, I have yet to see one in the flesh. I am basing my interest on the various reviews I have seen. jfeb' any particular reason you sold yours?

I'm 6'5" and have a 19.5" scandal, I prefer it to the 21" inbred I had before, they have long top tubes!

6'2" here with an 18" Scandal. Perfect fit

6'4", 36" legs and had first ride on a 21" with 90mm stem today – felt spot on but I like 'em long (shunted seat right back). 20mm shorter top tube if you go down a size….
Hasn't helped has it?
In the Lakes if you want a spin.

Thanks for the input guys. Had the tape measure on my existing bikes and it looks like the 21" will be correct leg wise but the extra 20mm ETT length may be an issue….

Thats the original Scandal 21" set up for me at 6'7" with a 40" standover – it doesn't look a lot of frame does it?

Ignore seat tube length. As long as the seat tube is long enough that you can fit on the bike with a 400mm seatpost all that matters is the ETT (or "front centre" to be more accurate). 20mm extra is loads IMO.

I sold mine only because I couldn't justify 5 bikes including two 29ers and one had to go. It is a great frame and I suspect I will regret selling it.