The ideal r290s are Midea clones (but with ideal controls) made I believe in china.

To the best of my knowledge Mitsubishi and Vaillant assemble heat pumps in the UK.  Both have a good reputation (as does ideal in fairness)

If it's fully pushed in yes, better if it also had some tape over the hole to ensure that circulating air didn't cool down the sensor.

You could take it out and test it!  There maybe a loose connection somewhere.

..could the dhw thermistor be connected in the wrong place?

Yes, or not properly pushed into the pocket on the side of the cylinder.

I know it's not 35 c as it's really hot out the tap

What's funny is the heat pump says its only using 21kwh a day but I know our normal use is around 10, so any idea where the remaining 20kwh might be being used?

I have a Logic Air 4kW heat pump and the CoP numbers reported are a work of fiction. It has been installed since November and the Halo Air is reporting a SCOP of 9.87. The main controller unit reports a different figure (though still wrong AFAICT). I complained to an Ideal engineer when he visited and he fobbed me off saying that all manufacturers' reporting is like that. I have installed my own custom monitoring now to get sensible data out of it.

The flow and return always seem a little too similar...currently 36 to 33 return.

What should target flow rate be, flow temp and return temp.

The manual says that the design flow rate for the 10kW model is 28.7 l/m so it sounds like your flow rate is correct. The heat pump uses a fixed flow rate which means the heat pump will control the difference between flow and return temp by modulating the compressor. If the difference gets too small, it will turn off the compressor for a bit. I wouldn't worry about these numbers too much, just tweak the w/c curve until it is achieving your desired temperature.

How many cycles should I be aiming for over 24 hours.

There are two kinds of cycles:

1) The room temperature exceeds some threshold and stops the heating demand. With the Halo Air controller, I think the limit is the set point + 1 degree. This limit only exists if you have room influence enabled. If you set the w/c curve correctly this kind of cycling should never or rarely happen.

2) There is still a heating demand from the controller but the compressor turns off because the flow temp is too close to the return temp because it can't modulate low enough. This kind of cycling depends on how well sized the heat pump is to your house and I don't think there is too much you can do about it. The Ideal engineer told me that up to 3 cycles per hour is acceptable in his opinion.

Is there anything else I'm missing?

If you have an idea of how much heat in kWh your house needs, you could try to estimate whether your heat pump electricity usage is in the right ballpark.

Once that's working well you can tweak, or not as you choose.  I'm running on pure WC and dhw once per day for 1.5 hrs (hysterisis 3C) but we don't use my dhw.

As to consumption, where do the various figures you quote come from?  I assume your meter and your heat pump.  To answer the question suggest you plot over a couple of weeks to give more insight, then it might be possible to tell.  Spot readings are almost impossible to interpret due to various sources of noise.