Let me start by saying it I'm happy it works, but it is a bit cumbersome.
Not sure if I can post feedback here, but the mods can move it around as they like.
The function could be implemented a little bit more user-friendly. The current implementation of DHCP is in 2 locations.
On the Status > Network > LAN you can see the lease table.
In Network > Interfaces > LAN -> Edit you can setup the DHCP and reserve IP addresses.
The problem is you need to copy the MAC address, and probably you want to copy the IP address and hostname as well. Meaning you would nee to open an extra screen to copy this info. Not great on site on a tablet (or worse) phone.
A beter (IMO) way would be to just make a Reserve button on the status page (behind the device), that would bring you to the "add new instance" page with those fields prefilled.
Another minor problem is that since the (latest firmware)? You can not use a underscore, space or dash for the instance name. Thats a pitty. Since it would allow for a bit cleaner bookkeeping..