I've had the pleasure of fixing their websites after clients want to move away from their poorly designed services.
Here's a great example.
Firstly they use WordPress which is consider a joke in the web world for the last 7 years at least.
Secondly they deploy web apps integrated into the wordpress sites. If their client wants to migrate away from WordPress to something like WebFlow they cannot because the provider they use one.com locks them in (dynamic ip domain routing blocks the WP site and other apps) and the web-apps deployed around WordPress are hooked in, instead of being seperate entiries (something you are taught in the first year of high school for coding) they are a mess.
All in all avoid like the plague. You'll pay the cost in the future migrating away from these guys.