GJ, cracking glass happens rarely. You're more likely to hear when glass has cracked than when it hasn't so it may seem more frequent.
It's just common sense really.
If it's too hot to put your hand in the flow, turn it down.
If there's a load of steam coming off, turn it down.
If it feels the same temp as your tank, turn it up.
If there's ice on the inside of the window, stick with cold.

Like a few have said-for the extra $-go for it.
Rich, where were you in Lincs? You could have subbed it to me!

Or come round for a brew.