Looks good, Richard. I reckon you could sell a fair few of those.
One thing I don't like about the over-engineered flow controllers I've had is that they require a battery in good nick. If there's any problem with the battery, they don't work (or at least the two I've had were like that).
And they needed calibrating when the temp changes. The extra cost in batteries and the fannying about really hacked me off. Oh, and what really annoyed me was when I once accidentally hooked up the crocodile clips to the wrong polarity **BANG**. I've been told it's easy to protect from this, but I kinda suspect they do this on purpose to make you buy a new one.
That's why I binned them.
I reckon there's a big market for simple - low cost - flow controllers, like yours.