Hey David - I have both - after losing the real ones to a severe calcium deficiency about 5 years ago.
I really didn't have any trouble talking - even right from the start. You might feel more comfortable with them starting out if you use an adhesive, especially on the tops, and especially if you're going to be singing.
Also, you'll find that you have to make adjustments eating. I can't just bite into an apple any longer - I cut it in slices and then eat it. Nuts are pretty much off my diet since they so easily get under the plate and cause a big ouch!!! They're not worth the pain!!! Fruits with small seeds - like strawberries or raspberries are a pain too - but not as bad as nuts. Corn on the cob is a challenge and I would never attempt it in a restaurant - at home it's manageable - but not too pretty!!! Tender meats are a must - chewing on that piece of steak that resembles shoe leather is better left alone. Chewing gum??? - forget it!
I think you'll find that you just have to make your own adjustments to get what is comfortable for you. Unfortunately, they will never work like the "real thing", but it's better than doing without any at all. And of course if you get any sore spots (which you most likely will), get back to your dentist for an adjustment.
Good luck!