I wouldn't say it's a introductory build, it's actually one of the more complex in internal mechanics among PGs.
Perfect Grades essentially exist on a spectrum, from great internal mechanics and mediocre outer detail and articulation, to mediocre internal mechanics and great outer detail and articulation. The older PGs valued inner detail, newer ones outer detail. The Strike is the only PG that is a straightforward blend with no real drawbacks, and resultingly is the best Perfect Grade ever made. If you get any PG before the Strike, you'll get something similar to the Mark II, only with perhaps a more insane wiring system. Among later PGs, the Red Frame is a solid choice, as is the 00 and Exia, in my opinion. I'd suggest staying away from the Strike Freedom, as the wings are designed in such a way that they will snap in half, unless you make the proper modifications. The Unicorn is alright, I found on mine I was unable to properly fit the shoulder raising joint properly, and as a result I couldn't raise the shoulder at an angle, like is seen in this pic, since the connection was too loose. Could have been a complete mistake on my part, but watch out for it if you choose the Unicorn.