Fair enough, I do NOT mean to scare away anyone posting cool new things and options, so thank you for doing so. My response was only so that new buyers of the HAS and OSSC don't spend extra money when they don't need to do so.
If you have a HAS, the D15 adapter (you're correct it doesn't convert a signal, just adapts the connector), which by the way is an extra cost and you have to order it separately, you can play TAITO F3 games fine on an OSSC. The only thing you'll miss out on is the OSSCs low pass filter, as AV3 on the OSSC does not have it. But it's not really needed for F3 as the HAS has you covered.
IMO, you're just getting something extra that doesn't do much for you, but the adapter itself is very cool, useful in many other cases, and also helps with the OSSC not having a LPF on the AV3 input, as Bob mentions in the video. It's a cool thing, you just don't need it for the HAS!