@glasgow -
Gen 1 Smart meters can be used with other providers - but they do become ‘dumb’ (i.e you need to manually read the meter and send the details off to the new supplier) when you switch. SMETS2 meters are coming ‘soon’ (later this year/start next year) which are multi-supplier compatible (for some reason I cannot fathom, the incubant suppliers seem to want to encourage people to get the old SMETS1 meters and then tell people they are now locked to that supplier…). 
I’ve been with Bulb about 7 months now and I’m quite happy with them - they’ve had two price rises in that time (but I think most of the others have as well) which they’ve let members know about 60 days+ in advance (usually a ‘if utility prices continue, we’ll have to raise prices soon’ notice… then next month…‘yeah, we’re going to have to raise prices - existing customers get 60 days notice’: l am aware last year they put prices down a couple of times). Bulb have NO exit fee: so if you aren’t happy with the new prices, you can just leave.
Oh - and if you switch to Bulb using an affiliate link such as mine - https://bulb.co.uk/refer/richard6920 - not only will the referring member get £50, but you’ll get £50 credit as well AND Bulb will pay your existing suppliers exit fee up to £60 per fuel (£120 total) - https://help.bulb.co.uk/hc/en-us/articles/115001227591-What-about-exit-fees-from-my-current-supplier- (Bulb will actually do the latter even if you sign up directly, but using my referral link is the preferred way for me )