The Grendel was the combination of the smallest and lightest .380 pocket piece at the time. Forgoing a conventional mag and grip was intentional as part of the weight and size savings.
It could be charged quickly with .223 stripper clips as they have the same case head size as .380 IIRC. Not really any worse than a non-moon clip revolver IMO.
Not a great success, I agree, but not everyone is JMB, and you don't get anywhere if you're unwilling to take a chance. Fortunately Kelgren was able to capitalize on the mistakes of the Grendels and apply what he learned to the Kel-Tec's.
Obviously the debeut of the Kel-Tek P3AT worked up via the P32 is the same concept, but with the more conventional design, and probably even smaller.
Greg's posting is the very unusual Grendel P22, a 20 shot .22 magnum with a conventional magazine arrangment.