Ubiquity for small non-profit offices question: USG? With or without a UTM?

Greetings!

I work with a non-profit with several small offices around the world in developing nations. We’re trying to “unify” things, and the Unify line is what meets our needs and our budget.

I’m trying to balance ease of remote management (from a time/efficiency and usability perspective) with security and future room for growth. I know the USG is limited in terms of its feature set verses most UTMs (Sophos, Meraki, SonicWall), and the hardware wasn’t designed with IDS/IPS and DPI in mind.

BUT, we don’t need a lot of the advanced features of most UTMs. We have machine level content filtering, AV, and phishing. Buuuut, for a better layered approach, I know a UTM would be best. But, is this overkill for an office of 15 staff with only workstations?

Any thoughts? USG only? UTM only? Both?