There is simply no comparison - the SRM conversion is far, far superior to the original bush. If you ride an A10 or A7 in a low level of tune and are not prone to thrashing it, then fine, the bush will usually suffice. Once BSA uprated the power though on the late A10s and the later unit twins, the bush was at the absolute limit of acceptability. BSA had loads of warranty claims, and many unimpressed customers. The bush can't cope with high revs & power.
My A10 is tuned up, and has been thrashed continuously for the past 34 years. The bush lasted two years, but the SRM conversion has managed 32 years so far - with one replacement a few years back as I'd stripped it anyway.
My bike does a lot of miles, cruises at 80mph on faster roads, and gets revved high through the gears all the time. No bush could cope with what I've put my engine through. You might consider me a philistine for treating my BSA like this, but it's built to take it. If you only potter round on yours (and there's nothing wrong with that) then don't waste your money on an SRM conversion. If you want a bullet proof engine like mine, get the SRM conversion, and nitride your crank at the same time.