The monitors work, but IMO they are unnecessary. We have one as apart of the solar installation, and other than giving me smug satisfaction that I am getting free hot water in the summer AND being paid for it, it is pointless.
If it runs on electricity and gets hot, or is loud, it will be using power.
Your problem will be the heating. Our electric underfloor (only used when we are away and not feeding logs into the Rayburn) runs off a 4 kW electric boiler. Yours may be wires, but the load will be similar. A 4 Kw system running for an evening will be using probably 16 kWh - £1.60 or so. Another few kW for your rad and you'll be at £2.
Turn the target temperature down and your bills will reduce. It's as simple as that. Ditto with the dryer. Switching underfloor heating on and off is not a good idea - it is all about long slow heat and the thermal mass of the floor. If we switch ours on from cold, it runs very hard for about 12 hours, bringing 60 tonnes of concrete in the floor up to target temperature. You're then warm for a week. Once it is running, its all about target temperature - how frequently does it have to work to maintain the temperature.
On the flip side, you're spending the price of a latte to have have a nice warm house every day. Crack on.