There are currently two different sorts of bottom surgery that offer different results. I won’t go into detail here, you can do research yourself about that if you wish. To put it basically, you can get a larger penis (phallo), or a smaller one (meto).
Assuming the surgery was successful for phallo, if you got up close to have a look, I think you could possibly notice some differences. At a glace at a urinal or change room, you wouldn’t notice anything. Like all surgeries, there can be complications and some guys do lose tissue, and even their entire penis, usually to infection I believe, but don’t quote me on that part. I can’t say that for a fact. I haven’t talked to guys who have lost tissue about how realistic their penis looks and how well it passes, although I have seen photos myself and they really vary. If they covered the part where they lost tissue, I wouldn’t question it. I have also known of some trans guys post phallo who have had sex with people unaware of their trans status, and they didn’t question anything, even when they got a good look at their penis. I’m not how to answer this because people will react in different ways. I showed my dad photos of phalloplasty results once, explaining that those were my options in the future for bottom surgery, and he was groaning about how fake they looked, but he was always harsh on me about surgery results until I had my own. Maybe you should look at photos and judge yourself.
With the smaller option, the meto, it’s more comparable to a micropenis. A lot of guys who get this surgery can’t pee standing up because it’s too small, so they use a stall or a stand to pee device. I follow a few guys online who have had this surgery and I don’t know any of them who hook up without disclosing their trans status. With the phallo option, more guys have the freedom to be naked without worrying about what people will think because it looks closer to the average penis. Guys who get meto don’t have the same freedom because of the size, so I don’t actually know any guys who have had this surgery and can talk about their experiences the same way some guys who get phallo do. Here’s my opinion, anyway. If I saw a trans man who had got meto, and I didn’t know there was such thing as bottom surgery, I would think he either had a micropenis, or an intersex condition.
I also want to add that some people don’t get surgery, or can’t, and they may use a prosthetic penis. Some of them are extremely realistic.
You can look at my helpful stuff page to see photos of surgery results and some prosthetics.