Those stingers look good -- effectiveness of a kubotan with the stability and natural hold of brass knuckles. All that for $10. It does require that you be already in grappling range.
I carry an ASP key defender. It serves quadruple duty as key chain, flail, OC dispenser, and kubotan. It works at a variety of distances and works as a distancing weapon. The disadvantages are the greater price (about $25, plus routine replacements for old OC cartridges) and that, at 5-1/2" (not counting the keys), it's a bit unwieldy. I just found out ASP makes a shorter one, a palm defender. I may ask for that for my birthday.