Thermostatic vs Non-Thermostatic Shower

My landlord's plumber has ordered a replacement for a scaled up Bristan Pisa shower by ordering a Java. Now, I didn't think at the time but the price was so cheap I've just checked the net and guessed that the Java is a non-thermostatic type whereas the Pisa was thermo.

The hot water runs from a Poxi Batterton 130HE with very high pressure but not terribly impressive flow and I wonder what the risks are of replacing a thermo with a non-thermo. Anyone?

Ta
CDG

(Raised in Appliances in error first - needs deleting there but could really use a quick answer)

more risk to the old/young .....and the wealthy who`d sue do the wealthy rent

I've told him to order the thermostatic and let the landlord know (he's very good like that!). It's an extra 200 notes of course but the labour is really good value.