HAS has a great feature which I won't implement, button remapping.
Other than that I'd say we're on a similar level now, with a few subtle differences.
I'm using ATX as the main power connection which brings certain advantages like being able to utilise a power switch on the supergun itself and use of a Pico power supply. I've also incorporated onboard negative 5V generation to cover ATX supplies that don't have it available, HAS wouldn't need this feature as RGB has designed it around using an arcade PSU which generally have -5V available. My supergun has the option of utilising an arcade PSU via an additional wiring harness.
Mine uses a Mega Drive 2 / Genesis 2 RGB scart cable for both video and audio output. HAS uses an 8 pin mini DIN cable for audio and video output with the option of a 3.5mm headphone connector for separated audio output.
I have a dipswitch to enable / disable buttons 4,5,6 from the jamma edge.
Both have composite and s-video options available via a separate accessory PCB.
Both have 3P/4P adapters.
I've got Snes and Mega Drive controller adapters whereas HAS has Saturn.
Both are UD USB compatible.
I think that covers most of it, though some info may be inaccurate on account of an awesome new HAS design being revealed and I don't yet know what features RGB has added.