I’ve got a 650b and a 29 set both fitted and in use. I managed to source the 650b one in the UK from my LBS when he had limited stock and the 29er one came from mantel bikes in the Netherlands (great service and unbeatable price, highly recommended).
Still early days yet, set up was a fine, but as long as your on wide rims and methodical its not a problem, and I’m liking the security from rim strikes on my cheap Chinese carbon 29er rims. Only downside is the extra rotational weight and spending time finding tyres with strong enough carcasses to run at lower pressures so they don’t deform in corners.