I took a tour optional flight. But it was in my earlier travel days as a mature woman, so less intrepid than now or younger. Also, because it was 50C and I still remembered a tour bus catastrophe on the road to Abu Simbel. It was an Overseas Adventure Travel bus crashed into a parked truck...in the dark. There were deaths. This had occurred within months of my travel, so it was fresh in my mind.
For the road transfer, one leaves early in the morning before light and it is a lonely stretch of the road. I expect things have improved.
In January, temps will be lower, but darkness slightly longer. In my experience, 4 hours is plenty long enough for the site.
There was a post here in July 2024 that also discusses how to get to Abu Simbel. Have you read that thread for options? You could look at booking flights and taxis/drivers independently.