Currently, I use bespoke hardware for running UTM 9 (and I'm not familiar with the differences between the various Sophos UTM appliances) but I did recall seeing a similar question asked a few years back (it piqued my curiosity as I was thinking of buying a used Sophos UTM box to configure as a maintenance spare unit; it's still on my ever lengthening 'to-do' list) and having had a quick search, I found the thread (in this case, referring to a SG115):
An alternative that will keep the front LED panel active is described in ASG 425 Display with home license. UPDATE 40 minutes later - I just remembered that there's no LED on the 1xx series.
If you have a 300Mbps WAN connection or faster, you might want to consider eBaying the 135w (someone with a licensed 135w can add a hot spare that provides failover in milliseconds for no added licensing cost) and getting a white box with a more-powerful CPU. Check out UTM HCL and the last few pages of *Unofficial* Hardware Compatibility List (HCL).
Cheers - Bob
Sophos UTM Community Moderator Sophos Certified Architect - UTM Sophos Certified Engineer - XG Gold Solution Partner since 2005
