Brandon Mann signed a MiLB contract with the Nationals. Mann has pitched the last two years in the NPB for the Yokohama Bay Stars. He was used mainly as a reliever in 2011 and mainly as a starter in 2012. Overall, he threw 92.2 innings in the NPB with a kwERA - of 113. For obvious reasons (kwERA just involves strikeouts and walks), I didn't include park factors when looking at kwERA -, but when looking at FIP -, I did include park factors.
The Yokohama Bay Stars park regressed park factor over the last two seasons has been 115. I only wanted to look at the last two seasons because that is when the ball changed and I think the variables of the pre-2011 NPB makes it really hard to compare the two, as they are basically different leagues. However, from 2006-2010, it wasn't that different, with a 113 park factor, meaning that offense was suppressed at basically the same scale for Yokohama's park as the rest of the NPB. Just from a cursory look at the park factors, it seems this was basically true across the NPB.
Mann had a 3.69 FIP in his two years in the NPB, while league average (in the Central League) FIP was 3.46. However, when you adjust it for the park, you would expect the average Bay Stars (assuming half of their games are at home and the other half are at parks that roughly average out to be average) pitcher to have a FIP of 3.72. Using this crude method, Mann had about a 99 FIP - in the NPB.
The big problem is relief/starter splits, which it seems we don't have unless we want to manually go back and input them for the NPB ourselves. I don't want to do that for this post, so we will just go with the statistical fact that Mann was average to below average in the NPB, depending on whether you want to include home runs or not. Considering that he split his time between reliever and starter, you would expect him to be better than starters and probably a little better than the mean. He really wasn't, so there wasn't a lot to like about him from a statistical standpoint.
Mann is a 28 year old left-hander that was drafted in the 27th round by the Tampa Bay Rays back in 2002 (when they were still the Devil Rays obviously). He would spend multiple years in A-ball, and miss all of 2007, but reached AA in 2009 where he posted a 4.87 kwERA mostly as a starter. He would split 2010 with the Dodgers A+ as a reliever and the Atlantic League (Independent ball) as a starter before going to Japan.
According to NPB Tracker, he never reached 90 MPH on his fastball and averaged 88.2 MPH with a slow curve (~71 MPH), along with sliders and changeups that averaged about 80 MPH. It also seems that he added a 2-seam fastball ("shutto") in his 2nd year in the NPB (his worse year, in which he was a starter). As far as MLB starters go, there isn't a great comparison when it comes to pitches and velocity other than Bruce Chen, though Mann's fastball is slightly better. When looking at non qualified pitchers, Eric Stults is very similar (though his curve is a little slower) and maybe Chris Young with a few more MPH on the fastball is another comparison.
When watching video of Mann, you notice that he has a fairly standard delivery that seems easy to repeat and comes over the top in a 3/4 delivery. Even though it seems that the Nationals do need a left-handed reliever, it would be really surprising if Mann makes it out of spring training with the big league club. I see him starting the year in AAA.