the bic z4+ is one of those pens that really, at least for me, has a specialized job. but i'm getting ahead of myself.
as you can see in the illustration above, there are two different designs, the upper being the current incarnation, i am not entirely sure you can still find the original style. the good news is that they may look different, but in terms of quality they are identical.
the z4+ has a comfortable rubber grip that makes using it a bit easier on your fingers, the flow and glide are excellent, the bit is average. what makes this pen stand out is that it is a perfect inking pen on larger scale pieces, this pen bleeds ink, literally. the dark value of the ink makes an all or nothing pen, there is no middle ground, the ink does bleed through the paper, especially when you're laying it on thick, this pen is great at inking over pencils filling in black and outlining things. i personally wouldn't use it as a writing pen as it does bleed and there are better pens out there for that. now, if you're talking about large letters that is a different story, like i said, awesome at outlines and dark as pitch.
the prices vary depending on where you are looking but if you can find one for around $2 a pen or so you're doing well. as far as whether or not you should buy one... well if you like hand inking this pen is capable of better fine detail than say, a chisel or calligraphic pen, so yeah, go, buy one... if you hate it send it to me and ill send you a drawing back in exchange