Purely my opinion.
I found using it pointless. It doesn't make you last longer. You still climax within same time frame. The difference is that after you have climaxed you do not need to be stimulated much to regain/retain an erection.
When I've used it before, after cumming, I psychologically blocked out being aroused again and I could actually prevent myself from retaining hard on. Some mates say they have hard on all night. I'm not convinced to be honest.
Regarding buying it from pub toilets, you won't get viagra from a machine, but there is likely to be someone in there that can obtain it for you at a price.
Have you looked into arganine amino acid supplements? Increases dilation of blood vessels and blood flow.
Practice delay tactics when alone, not only does this give for amazing climax sensation but assists in controlling when you cum. Once you know the vital signs you are going to climax you get to know your point of no return and can do things to prevent climax.
Practice makes perfect hehehe
If your partner knows how to arouse you after climaxing, to get you hard, then it will get harder quicker and may go longer then, but that's just the same as good sex.
If taken when drunk, may well find you last longer, you may also find that you can't ejaculate at all until alcohol wears off. Taking viagra is ok. But there are so many other better ways to last longer and assist in wife's climax and enjoyment.
Longer foreplay use of toys, delay tactics, delay spray, change positions.
I certainly wouldn't get a complex about it. If you start to read into the actual time most men take to climax you will be shocked at how short a time it is. Which really highlights why foreplay is essential in good love making.