I'm going to be purchasing an AR15 soon and was curious if the 50BMG uppers are any good? Any comments would be appreciated.

Good news!
You picked a great time to shop for a .50 BMG upper.
Years ago the only game in town was the Watson upper. They are accurate, but they have a screw in breach, very slow to load and unload.
These days there are some really good bolt action .50 BMG uppers out there.

Known to me are:

The Ferret .50 I know Dave Moore, the owner, personally and have shot with him a few times. His product is top notch and so is his reputation for customer service.

The Ultralite 50 This upper is compact and light, but it doesn't have an overpowering recoil. I also know and have shot with the designer of this upper, Dennis Chaney. The quality of his work is unbelievable.

The Ultra Mag 50 Dennis Chaney and a friend of his, Dave Finnie, developed this mag fed upper together.

The Ultra Lite and the Ultra Mag are manufactured by two different companies, but both Ligamec Corp.(Ultra Lite 50) and Safety Harbor Firearms (Ultra Mag 50) have fine reputations.

Advanced Long Range Systems I don't know Darren Wardle at ALS, but his uppers have a reputation for high accuracy at the matches.

If you are interested in long range accuracy, the Ferret 50 or the ALS both are bringing home the trophys in the FCSA's Hunter Class. All of the above products are well made, by companies who know the value of reputation. Good luck, with whatever you choose.

Great, thanks for the info.