I had BT 36 Mbps FTTC for many years, and generally found it to be satisfactory. I decided to move to Swish because I was out of contract with BT and didn't want to sign up to a new BT fixed length contract; also the rising price of BT Broadband exceeded the Swish price.
My house is in a private road, that was always going to make access more difficult - getting permission to dig trenches etc. Swish genuinely seemed keen to be my provider, even though getting to my house was always going to be more challenging than from a public road. Using existing BT route was explored and found not to be viable due to collapsed trunking. Fortunately access was possible from a nearby pole and only took a couple of hours from the 2-man team arriving to having a working service.
EDIT: I'm now a year in, and still no complaints; I get the full advertised speed, am not aware of any outages, so I am very pleased I moved to Swish. I am now out of contract, and to my surprise, if I sign up for 18 months, I will get all the perks of a brand new customer - 6 months free and a free router of the latest type. Currently (Apr 23) Swish are offering their fastest speed for £50 instead of £75 per month.
The MESH module originally provided is esoteric - a Plume pod - https://www.plume.com/serviceproviders/products/homepass/. I believe a Linksys Velop router is about to be offered as an alternative.