I was using it for 1 year and only recently switched out.
Yes it is still based on DSL, but the copper wire has reduced from their switching facility to the lawn fridge; it is all fiber from there. So speed wise it can go up to 55Mbps or so if I really want, but I only signed up for 6Mbps because that's cheaper and fast enough for me.
You do not need a landline phone service for that. It is reliable I've only been down for an hour once. I think they have their modem that they can log in to diagnose line quality so it probably helps.
You do need to rent their modem instead of buying your own. Last year they force me to rent unless I pay for the higher cost service. This year they just raise the price and make it $40 for 25Mbps instead.
I'm at Comcast and it took me 2 weeks to install, their tech support never called as promised and I was hung with a used modem stuck in another account, CS entered the wrong modem ID/MAC/etc for a long time. But it is $10 cheaper ($30) for 10Mbps when I use my own modem ($20 used from ebay).