.50 Cal barrel conversion for a shotgun

Buddy of mine has a Mossberg Maverick 12ga shotgun. He is wanting to get a muzzleloader, but also wants to save some money. He has asked me what I thought about getting a .50 cal barrel for his shotgun ($130), see attached link:

http://www.midwayusa.com/viewProduct/?productNumber=861787

I don't have any experiance with this conversion. Wonderning if anyone had any input/suggestions, pros and cons. I told him if it were me I'd just get the Wolf at Wally world for $170. But I don't know what I am talking about, so any advice is appreciated.

Thanks