I have the Gosson Profi Six. I bought it new 20 years ago and have slowly but very cheaply, added the accessories to make it into a complete system meter.
I have the 1º 5º 10º spotmeter attachment. The attachment is a bit bulky, but at $25.00 worth it.
The darkroom attachment, which converts the meter into an enlarging exposure meter, $5.00 at a photo flea market, works exceptionally well!
The profi flex, fibre optic measuring attachment. This turns the meter into a ground glass TTL meter for large format, or measuring stuff in tiny holes, $15.00. (also turns the meter into a densitometer)
The Repro attachment, designed for measuring light falling onto a flat painting or art surface, for reproduction work, $5.00.
In all, there are ten accessory attachments that really make the meter work for all facets of photography.
One of the most popular accessories, is the 7.5º - 15º semi spot meter attachment. This is often traded for about $25.00.