I agree with Grandad..
There are some cheap Gent (JR Gent) kits but they are very often entry level and good to start off with to learn with.
But the better quality are as Grandad states along with some kits sold by turners retreat, turners workshop and Axminster to name but a few.
Main points with a FP is to make sure that the nib is screwed in position and not interference fit. Makes it easier for the customer to change the nib and easier for you to up-grade the nib to a higher spec such as the Bock supplied in the UK by Beaufort (Phil Dart)
And don't just accept that the supplier says yes you can change the nib, ask if the nib section is threaded..