I have sot many of the BFR revolvers, when I worked the booth at the Sportsman Fair in Corona. I do not recall a 30-30 being there but we did have 45-70 and at one point a 450 Marlin and the 22Hornet, and a 500 S&W.
The Sportsmans fair is a tourture test for these guns. I can tell you the full house 500 Loads after three days sheared the screw holding on the ejector rod. The 45-70 held up for many years in the hot sun with a water truck occasionally wetting the whole shooting line and the fine dust, hundreds of rounds of ammo, no cleaning, no grease or oil, and sweat of all the shootinge and grime of the range officers loading the guns for the shooters.
Back to the guns. I think they are more of a novelty than a side arm. If you are going ot use it as a hunting handgun that is a different story. Having the gun out as a primary arm as opposed to lugging a huge handgun along that will be dificult to remove from a holster with small movements, so as not to attract attention from your quarry.
When we were shooting the H&R Bufflo classic at the same time as the BFR both in 45-70 we had a mix of ammo, some being 405 grain cowboy loads and some bing the 300 grain JHP factory loads. The 300 grainers out of the rifle were stout and the 405 cowboy loads were easy with the black powder loads. The BFR was the exact opposite the 300 grain was little recoil but a huge flash and the 405 was a puff and a lot more recoil. I think you are going to have a problem loading one 30-30 load and getting top proformance out of both the rifle and the handgun.
I think a Ruger Black hawk in 45 colt, 44 mag, or 357 mag would cost about 1/2 as much and be more usefull as a side arm.