Homeserve got a worse review than BG. That customer featured got stitched up by BG. Even if it was grav HW the only "upgrade" BG would normally have done would be to add a tapstat on return for a nominal fee. I wouldnt have paid if i wasnt told it wasnt covered on 1st inspection. A cylinder is hardly hard to spot
To be fair WB are the only ones to come out with any credibilty. It does mention that BG cover is littered with exclusions and they do always insist on powerflushing and upgrades even when not reqd.
"Which?" also filmed 10 engineers recently one of which was a BG guy who didn't do the job properly and has been reported to Gas safe!
Only 1 that did a pukka job was a self employed rgi and he was the most expensive (but worth it imo).