The UDM line is about a year old and many features are in the "to-be-implemented" bin. This is a vague statement and I don't have specific examples on hand. I just recall seeing references to them when hunting around. I don't have firsthand experience.
The UDM can't be adopted by another controller: it needs to be the unifi controller. This really kills the upgrade path imo.
One of my best metrics for deciding what hardware to get is to look through the 1-star reviews for realistic testimonials by reasonable users. It takes a lot of sifting, but it builds an okay picture. There are almost no complaints about the ER-4 compared to the UDM. I think I'd likely roll a pfSense box before jumping into unifi.
I got a UDM-pro and overall while i am very happy with the other unfi gear i have i would have not gotten the UDM pro if i'd known about the limitations before hand: can't adopt USGs to its controller, link agger doesn't work ("yet" so never), and IDS/IPS maxes out at around 800mbps and i have gbit now so its limiting my internet.
i'd have gone with a USG-pro and cloudkey 2, but otherwise the unfi ecosystem has been good, i like the single plane view of my network and works well enough to not want to give that up
The UDM can't be adopted by another controller: it needs to be the unifi controller. This really kills the upgrade path imo.
One of my best metrics for deciding what hardware to get is to look through the 1-star reviews for realistic testimonials by reasonable users. It takes a lot of sifting, but it builds an okay picture. There are almost no complaints about the ER-4 compared to the UDM. I think I'd likely roll a pfSense box before jumping into unifi.
https://www.amazon.com/product-reviews/B081QNJFPV/ref=cm_cr_...