Yeah - the hybrid cloud and on-premises build agents is actually one of my favorite features. The open source project that I help maintain (libgit2) uses VSTS's hosted Linux, Windows and macOS build agents, but add support for some other platforms (like ARM) with on-premises build agents.
("On-premises build agents" makes it sound fancier than it is, it's actually Raspberry Pi's on my desk, but hey, whatever works, right?)
It would definitely help to see comparisons against competition, e.g. GitLab, CircleCI