So I'm not remotely near the UK but y'all have an awful lot of good discussion in here.
@The Bedroom Gardener UK - Interesting device, I was just reading up on something similar. Might be worth a look for comparison. Several models but here is the canna specific version. A terrible 999 for price.
Don't have time to send your cannabis to a lab? CannaDX is a portable cannabis chemical analyzer that will test the potency of your flower for THC.
www.mydxlife.com
@EP3 - I have an inkbird temp/humidity controller. Has worked decently. Not always accurate but if you have a calibrated device and can work off the variance it's pretty good. I have been using the ITC-608 as it has two plugs and two different sensors. One for temp and one for humidity. Plug both heater and humidifier and it holds the tent at pretty steady temp/rh. A little bit of swing but it's way easier than trying to program another timer. Another plus is you can get a cheap humidifier and let the Inkbird do the on/off adjustments as needed. No fiddling. The nice humidifiers have those digital buttons, you want a cheap one with a mechanical on/off switch if you go this route. Same with the heater. No readout panel, just a dang on/off and let the power strip do the work.
ITC-608T Temperature&Humidity Controller(3 in 1 Multifunctional)
www.amazon.com
I highly recommend a good tobacco hygrometer that is adjustable. Get a Boveda calibration bag and get that hygrometer calibrated. Then you can work off that for your grow and making adjustments. The cal bag lasts a year or so. You can check your devices with it once a month to keep things in line. I know I'm overcomplicating it but I've got time to putter around the house. Once things are set it is nice to know that all I have to really do is check, water, and not get in the way.