Hello and welcome. Of the Sats, the 250 will be smoother than the 500 but the 500 has a clever suspension set-up so try-before-you-buy.

My wife has pretty severe scoliosis - seeing a chiropractor constantly. I bought her a tilt table and it's made a huge difference. She hangs upside down for 10 minutes a day and life is good.

Mmmmm, hang the wife upside down, now there's a thought - and I can't seem to shake it

Oops, double post, stupid phone

Instead of sealant in the bars, try gravel, sand would be light.
If your near Blakpool you can try my twin 650 Burgman