Originals are somewhat slow to load. Generally, there is no problem stripping in the first 15 from chargers but, after that, things get pretty stiff. I have loaded mine up all the way (once only, out of respect for the old spring) and those final 5 rounds were very difficult to load and almost as difficult to feed; you really have to slam that bolt.
Mine is an original B/N marking: Bing of Nurnberg, the famous toy manufacturer..... and it is definitely a toy!
On the Western Front, these magazines proved troublesome enough that they were withdrawn from Service late in 1916.
In the East, however, the war proceeded along less-insane lines to an extent and the magazine extensions retained some utility there. My friend Jack Snow (Newfoundland Regiment) told me that he saw some of these still in use by the Imperial German Army as they were pulling back into Germany prior to being sent to the Western Front, following the Treaty of Brest-Litovsk. Jack would have been quite close enough to the German troops at that time, he and his two comrades having surrendered to the retreating German Army only about 40 or 50 miles from Smolensk. Supposedly they were under close guard, but nobody really wanted to get off the train; the countryside was swarming with Reds, Whites, Greens and Blacks, all engaged in a frightful game of massacre/countermassacre. "Fritz kept us drunk, all the way back to Heilsberg," said Jack. At Heilsberg the three escapees were dropped off, tried, did their 30 days on bread-and-water (it was supposed to be solitary confinement but they were 3 to a cell because of the number of returning escapees and prisoners on punishment) before being shipped back to the very estate from which they had escaped, to work as agricultural labourers until the Armistice only a couple of months later. But Jack was quite certain that he had seen a number of these magazines still in use, approximately September of 1918, while they already had been withdrawn in the West well before the Newfoundland assault at Monchy-le-Preux in April of 1917.