I don't have any DB-mounted Shellys. My go-to for a DB-mounted switch/power meter used to be the ZMAi-90 - I have 4 of them from two different hardware generations installed in my own DBs and have flashed several for friends. They used to be really easy to flash, but the most recent ones I've received (late 2021) have had non-ESP-based WiFi modules, so they've required that I swap out the module for an ESP-12, which is relatively easy to do with a hot air station, but it does add some cost and hassle.
Since the ZMAi-90s stopped using ESPs my next generation of high power meters were DDS238-2 switches. Like the ZMAi-90s they're also 2 DIN units wide and have a small LCD on the front which gives you some local feedback on voltage, current, power, energy, etc. Unlike the ZMAi-90s they have the slightly unusual setup of neutral connections at the bottom and live in and out at the top, which a slight negative in my mind, but on the plus side they still (last purchase a few months ago) come with ESP-based WiFi modules so you don't need to buy ESP-12s for brain transplants. With the original ESP-powered ZMAi-90 the original flashing guide you'll find online covered the fact that you'll need to hold the main microcontroller that actually does all the power measurement in reset to prevent it from spamming the serial bus and preventing flashing. The DDS238-2 uses the same main micro, so it has the same issue, but I wasn't able to find a convenient point on the PCB to tie low to reset that micro. The upshot of that was that I found it easiest for the last batch to remove the ESP modules with hot air and flash them separately before reinstalling them, so they're still a bit of a hassle to flash. Another issue that the current generation of DDS238s and ZMAi-90s share is that the main micro doesn't report updated figures to the ESP often enough for me. You can solve that with a Tasmota timer rule that polls the main micro every second, but that comes with the side effect of annoying MQTT spam because I haven't found a way to stop Tasmota from reporting serial success over MQTT.
The single-DIN-width units covered in this post are a LOT easier to flash than either of their double-width cousins above. Once you've bent the rivets holding them closed, they're easy to open and the ESP-based WiFi module is easily flashed in situ - it just requires some soldering of thin fly leads to the board (30AWG wire wrapping wire is great for this). I was initially a little sceptical of anyone claiming to get a beefy enough relay into a single DIN width unit, but the having seen these ones I think they're plenty beefy enough for to be trusted up to at least a third or a half of their claimed 63A rating. They seem to be sold under lots of brands - The SMTONOFF still appears in Banggood ads (about $27), but I've seen them listed as REVOLT or RED POLE on Takealot (both at R699). I've only flashed one REVOLT-branded one for a friend so far and it isn't installed yet so I don't have much real world data, but in my basic testing it performed well, readings were pretty accurate and updates snappy, so I'm likely to start using these more frequently. The space saving of a single DIN width is a great plus too!
