It seems like the standard pen case for the Lego pens at the turn of the millennium. (Although I guess it's missing the plastic backing that would hold the spare beads on display.) A cool design bit is that the top is somewhat shaped like a Bohrok faceplate.
(Click for larger images)
The leaflet shows off some of the other various pens, including the original Toa Mata pens, the rest of the Bohrok pens, and a collection of the Toa Nuva pens. (I have the masks from all the Mata pens, but I haven't found any of the Nuva pens. There are a few available online from ebay and such... but I think they're going for $40 to $60. So that's a no from me.) There are some quirky descriptions of the pens (with a tip to add them to your collection ASAP, subtle marketing there) as well as a bio for the Gahlok Bohrok. (Which sounds vaguely familiar, so it's a little more official than the Mata Bios on the previous pen leaflets.)
The full pen can hold about six beads, and comes with a handful of extras to let you customize the design. I mean, neat concept, but Lego played that out for a ton of different pens back in the day, so it's not exactly revolutionary here. The grip is kinda cool with the swirly blue design. Alas, the ink is long since dried up (it's been 16 years now) and I have yet to find a replacement cartridge. (I have looked through a few craft stores... if somebody more knowledgeable knows anything, please share, it would be kinda cool to make these pens usable again.) The main unique feature here is the Bohrok faceplate. Unfortunately, it's attached to the top of the pen (and as such to the pin that runs down the center of the entire thing) so you can't really use it to make a mini Bohrok. But it folds up and down nicely to cover the krana and keep it from falling out. (Kinda.)
You get 11 beads plus the mini krana. The cooler beads, IMO, are the printed ones. The giant black one with the Bionicle logo appears in all the Bionicle pens, as far as I can tell, but it's still a decent design. Then you've got some medium blue beads with the Bohrok symbol, Gahlok shield, and a silhouette of the Gahlok Va. Then there's a blue bead that has an outline of the Mata Nui island on one side, and the name spelt out on the other. The rest of the beads are generic filler, including a blue, orange, trans orange, and thin medium blue bead (the latter of which it still on the bar in the image above.) The last large bead is actually molded after the Bohrok limb piece, which is clever.
Of course, the beads are largely superficial decorations. Yes, they do roughly fit onto a system stud, but there's no real practical MOC use out of them. Instead, everybody's interested in the krana and the head bead it attaches to.
The head bead does attach to a minifig neck... kind of. It attaches as well as any of the other pen beads, which is to say barely. Unfortunately, while the original Toa Kanohi hung down and covered the neck gap, the krana does not. (The head bead also sticks out quite a bit in the back, making it even more awkward to place on a minifigure torso.)
The krana is a hard plastic orange Krana Yo (the tunneling mole krana, for those who haven't memorized the powers). It has a small pin connection that fits exclusively into the mouth of the head bead. It is too small to fit into a traditional system bar hole, but too large to fit into the small accessory holes seen in minifigure hairpieces. Basically, it's useless without the head bead to attach to. And the attachment is weak... I don't know if that has to do with age or not, but the clutch power is barely there.
It's not to say the head bead is completely worthless. It attaches firmly to a stud, so it would actually work nicely to incorporate a small krana into a system MOC. There's potential... but not enough for me to go and track down the other five Bohrok pens. Unfortunately, it looks like the Toa Nuva pens also have unique masks that clip to the same head bead, which means that making Toa Nuva minifigures using the pen masks does not seem like a feasible project either, even if the pens were moderately affordable.
So the pen is only sorta meh, and the beads and krana aren't quite as worthy as the Toa Mata pen masks. There's a nice nostalgia kick for those of us who grew up in the Bohrok saga, but honestly it's not a must-have collectible.
And standard disclaimer: the Toa Mata masks pictured are from the *spoiler* Toa Pens from 2001. The torso decals were done by Nuju Metru (I gave him a handful of collectible minifigs for them.) I already did a post about maybe getting a bunch of torsos printed on commission, but there was no interest and instead people just griped about my color choices.)