Just buy pulse generator for 0.5$ (check aliexpress for "NE555 adjustable frequency Pulse generator module") and forget about devfee.
I built some pulse generators for other miners, so I'm fully aware of that route. 
This firmware gives me the ability to set frequency and voltage for each board independently, reaching >20MH/s average with almost no HW errors (though, I have to say D3 is very strange in regards to HW errors). In my opinion, it definitely worth the 1.5% dev fee. I'm not going back to stock!