I have iBoost+, it was installed by default when I had my solar/battery installed so I didn't have a chance to research it. Had I known at the time it wasn't modern and smart I would have have looked for alternatives...
I'm on Agile and as others have written, no point in using it if the export price is above your kWh gas price (so 7p/kWh for me).
As per KevinD I swapped the manual dual-pole isolator switch for a smart one ("Wifi Timer Fused Spur Wall Controller For Electric Towel Rail" from CompanyBlue). This allows me to schedule turning off iBoost+ between 4PM and 7PM (actually through to 10AM) when I get most price for export and don't want my battery heating water. You can use the Tuya App to control its schedules and also to manually turn on/off, and get power consumption figures.
It's worked fine even when its had just over 3kWh flowing through it to the immersion.
I have also deleted all the iBoost+ Boost schedules, and set the trigger threshold at 250W.
Also, iBoost+ doesn't easily allow me to make use of grid electiricity (Boost feature) when its well below the price of gas/kWh, as it is sometimes overnight. I think I might set Boost schedule on all night, and then use Tuya schedule to turn it on during the extra cheap times (aslo need to make sure batteries aren't discharging into it). A bit of a hassle...