Interserver is a great web hosting company and I've had a VPS myself with them for 8 years and have had very little issues.
There's of course been some outages, but that can happen with any other hosting provider as well, but the outages were fixed quickly and the support team also responded fast.
I've had like maybe 2 outages with Interserver in the 8 years I've been with them, so that is a great thing.
No outages would be best, but all hosting companies are gonna face some outages at some point.
Interserver VPS hosting has been very fast for me as well and it's also easy to upgrade to more RAM and storage and resources as your website grows.