I've taken Sildenafil (generic viagra) a few times before. It was an experiment, I'm easily aroused and get hard at the drop of a hat and no issues staying hard either. However, once I cum my sex drive drops to near zero almost immediately unless it's a special circumstance (like group play, etc) or super kinky. My wife's sex drive climbs with every orgasm regardless of the situation so we wanted to see if this would help match her energy during regular play. Here is what I've experienced:
1. Once it kicks in, I have a semi hard dick for a while (if you've ever taken pre-workout, basically its stim dick)
2. When I'm fully hard just sitting on the couch or whatever, it takes longer to go down
3. No difference at all while having sex
4. After I cum, I stay semi-hard for a while, but I'm not aroused
5. I can get fully hard again after a few minutes, but does nothing for arousal or interest in sex, its just going through the motions
So long story short, I tried it a few times to see if it helps maintain arousal longer (interest, not erection) or shorten the refractory period. It did neither for me. So if you have a physical need to get or maintain an erection, I'm sure it works great. But if you're looking for it to help rebound quicker or cum multiple times...good luck.