The Dorset Naga has had some deservedly good press on here recently, but even as an avid user I have to agree, they need treating with care.
There are different types of chilli heat. The restaurant heat is the small green chilli, and like others I add these liberally to curries, chopped, seeds and all. Scotch Bonnet is fruitier and in quantity, more savage. Expect a colonic call mid-morning.
Adding extra chilli powder will just give you a dry boring heat. I once asked my regular supplier the difference between his vindaloo and his phall. He said "chilli powder sir"
I then found a new local takeaway, dynamite hot, with that mid-morning urgency, so not one if you have to go to work next day.
I highly recommend the Dorset Naga, but please be careful