These new replacement rectifiers don't end up being much, if any, smaller than the originals once you add a heat sink but they are more modern, efficient, and much cheaper than motorcycle specific replacements. I consider the motorcycle specific units that some sellers charge $50 to $80 for to be a blatant rip-off. These $4 units that we use do exactly the same job for a fraction of the cost.
The new rectifier may give you a slight increase in charging output but for a real improvement, you should replace your antiquated mechanical regulator. This old stock unit works but it's output is very inconsistent, bouncing all over the place, up and down, regardless of RPMs. This works your rotor harder, making it jump through hoops to keep up with the constantly fluctuating voltage requests sent to it. A solid state automotive regulator works so much better and again, they can be had much cheaper than motorcycle specific units.