Tried them at one point to relieve the physical symptoms of anxiety for my exams. Not too sure if they worked. I didn't throw up though so I guess they did something.
Didn't really have any downsides except making me need to pee.
Basically with beta blockers it helps with the physical symptoms. So if you tend to get a tight chest or something when you're anxious they should help reduce that, but you will still have the same anxious thoughts.
So if you have anxiety about getting the bus because you think somebody will throw soup at you, you would still be worrying about the soup stuff, but wouldn't have the same tight chest, shaky feeling or whatever to go with it. That can really help because he physical stuff tends to be distracting and make people worry even more.
They can be a great tool for helping overcome anxiety because you're not having to battle the physical feeling so much and can challenge yourself a little more. Combining something like beta blockers with some form of therapy is a great method and one I would suggest you talk to your doc about if you're considering beta blockers.
Therapy can tackle the mental stuff while the bbs keep the physical stuff at bay. Once the mental has improved you shouldn't need to manage the physical any more because there's nothing to trigger it.
If physical symptoms aren't a big deal for you then obviously you don't have to take them and I believe you can also get them on an as and when needed kinda prescription so if you tend to be most of the time you can go without, but if you know you have a big thing coming up you can take one. That's how mine was sorted out.
How it's prescribed will depend on the person and the doctor though so do make sure you follow your doctors advice over anything I say.
Reading back it seems your focus is on presentations so sorry I missed that, but you should be able to appy what I said to that.
Basically if you get physical anxiety when giving presentations it could be worth trying bbs. You may have to take them a little while before to notice the effects and will still get any mental worries, but it could help.
Hope that helps. Sorry it's a bit of a read