I had RALP in March (full nerve sparing on one side, partial on the other) and have been on daily 5mg Tadalafil since May. Do read the leaflet, but I seem to remember it saying try to be consistent in the time of day you take them. Initially I had some muscle aches and a headache (which I think are common side effects), but that soon faded and now I have no side effects.
My wife and I are now able to have full penetrative sex without injections, rings or other artificial aids at the time. I would say my erection has now recovered to about 70% of what it was pre-operation.
I have been using a vacuum pump pretty much daily and would recommend that as part of penile rehabilitation. Even a cheap pump from someone like Love Honey will do the trick.
To be honest, my position 9 months post-operation is much better than I expected it to be, but it's clear this varies a lot between individuals and I count myself as one of the lucky ones.