I’ve got one somewhat similar that I inherited from my FIL. Don’t know if I’ve ever had it opened up. 

me too but havn't used it in years. i rarely use dowels anymore. it's bisquits or dominos.

Yeah and, honestly, if I use dowels I don’t use a jig. I glue the joint, then drill and dowel it. Of course, those are exposed, but if I want them hidden I use the domino. 

Lately, my ‘dowels’ have been replaced with small dia brass rod. Strong and a pretty accent to the project. 

I want to use dowels to make gluing up boards into a wide panels easier.

I am building my first cabinet which the plans call for a 12” x 40” for the cabinet sides. This is a hand tool cabinet for my shop.

I’ve never glued up two boards on their edge before. Seems like getting them aligned properly to minimize post-glue-up work would be a good thing. I’d hate to have it slip when I wasn’t looking for whatever reason.

Can’t justify buying a Domino for that purpose until maybe I have done it a few dozen times and am tired of fiddling with the jig.

For panel builds, you don’t need anything more than biscuits. They don’t add almost any strength, but they’re great for alignment. Honestly you don’t even need biscuits if your boards are milled flat and true, but if it’s a large panel it’s nice to have some alignment ‘helpers’. 

Dowels are really better used to add strength…they’re kinda a pain in the butt just for alignment, IMO. 

I have a 1980's Leightung dowel jig. Never use it, but the hardened bushings are great for lining a piece of plywood jig and using them to keep the bit vertical (and not chew up the plywood).

Dowels can be handy for joints where there is not enough width for biscuits/dominos, but damn if they don't have to be perfect for alignment since there is no wiggle room for adjusting.