We'll go Jones first, here's the numbers:
I firmly believe that Jones is an underrated player. The guy is terrible against left-handed pitching. For his career he's a .199/.237/.364 hitter against southpaws. That's awful. However, when he's been in there against righties, he's been good with a line of .275/.354/.483 and 46 home runs in 381 games. That's a solid line, especially for someone as cheap as Jones. Now that he has a right-handed backup at first base, we shouldn't have to see him in there too often against lefties, which only means positive things. I think he's a 20 home run guy easily this year and the batting average should come up because he doesn't have to face lefties as much. Obviously Jones isn't the answer for the future, but I think he'll play better than people expect this year and make fans not regret passing up on Derrek Lee. Jones isn't a great defender, but he's not terrible, and it really doesn't matter that much when you're talking about first base. All-in-all, I'm okay with Jones here. When you compare him to the rest of the league's first basemen, obviously there is a ton to be desired, but you can't forget the platoon.
The second half of this platoon is newly acquired Casey McGehee, let's check him out:
McGehee doesn't show the huge difference in his splits that Jones does. For his career he has hit .266/.319/.428 against righties and .261/.323/.420 against lefties. However, he doesn't have a very big sample in his career. Also, his 2011 season was just eery. McGehee hit .169/.228/.185 against left-handed pitching in 136 plate appearances. That is unheard of. There's no way he can repeat that kind of season against left-handed pitching. The guy was extremely unlucky last year, but obviously you can't blame just that for his awful 2011 season. There was definitely something wrong last year and it rightfully should make us all a little bit nervous. The thing that helps us overlook that was his solid years before that. In 2009 he hit .301/.360/.499 with 16 home runs and in 2010 he hit .285/.337/.464 with 23 home runs. He was fantastic with runners on base both of those years and eclipsed the 100 RBI mark in 2010 (in a juggernaut of an offense you might add). McGehee's 2011 season was scary, but if he can get back towards where he was in 2010, he'll be a very solid backup first baseman.
The main reason the Pirates brought in McGehee wasn't to platoon with Jones at first. It was to put some pressure on Pedro Alvarez and have him there in case Pedro doesn't get his act together this year and has to be sent down again. McGehee is primarily a third baseman, and a pretty good one at that, but he also plays a decent first base. He's a good depth guy to have, especially since the Pirates have very little in terms of other back-up third basemen.
All-in-all, when you combine these two guys in a platoon role at first base, you have yourself a decent first baseman. They aren't going to put up the numbers that Derrek Lee did last year in his hot stint with the Bucs, but they should be better than most people think. That said, you still can't give them too good of a grade, because they leave that risk of being absolutely anemic.
You can read the rest of this series here, or click the links below:
Catcher
Second Base
Shortstop
Third Base
Outfield