Fisheye Converter for Panasonic Lumix G Vario 14-42 X PZ

I bought this rather cheap converter for the 14-42 and test shots look pretty promising

http://interceptor121.com/2015/02/22/panasonic-lumix-g-x-vario-14-42mm-with-fisheye-converter-dmw-gfc1/

I think Nauticam tried this combo with the 4.33" dome and 30 extension long time ago with the OMD-M5 but have not seen anyone using it

With a cost of £95 or $125 this is something to try before getting the 7-14mm Panasonic in my opinion as it is very cost effective and seem to wok well also at relatively wide apertures f/5-f/8

What make this different then attaching a wet lens? The GFC1 is 120 degree, and become narrow once in water, but then the dome port restore it to what final FOV?

120 it's a dome port