I can't comment on the cooker itself but I think turkey or other poultry would be a good starting point. Poultry does not benefit from low 'n slow they same way that pork or beef does so if temperatures run a little on the high side, that's not going to be a bad thing.
You may not achieve the same results you found with commercially smoked birds unless you determine what process they use and copy that. I haven't done that. Maybe I should try. My birds come out more like a roasted turkey with some smoke flavor.
Of course you will want to get some chunks of smoking wood to add to the charcoal. A little mesquite, apple, hickory would add some flavor.
Also consider brining if your turkey is not already injected. I'm not sure what you will find in the UK. In the US most frozen turkeys are "enhanced with up to 12% special sauce" or something like that. It's basically salt water. Don't brine if injected.
A pork butt is also another good first cook as it is rather tolerant of a range of temperatures.
Good luck and post pictures!