I have a Jennings J-22. I have had it for quite a while. Maybe 15 or 16 years. It is very picky about ammo. Mine has gone full auto on one type of bulk ammo. Cant remember the brand. Velocitors and Stingers are some what reliable. I would be willing to pay $50 for one in good condition if all I had was $50 and I had no other options. However, I woould trust a.25 over a .22 any day. 25 is a center fire cartridge. It is much less prone to failure than the rim fire. If I were to choose between the two guns you are asking about Iwould go with the derringer. With the Jennings you might get more than two shots before it jams. Or it might jam after the first shot. With the derringer you will get two shots. I would not feel cofortable using either gun for self defense.
I bet you could finda used High Point for $100 if you really look around. They are not pretty. But they are reialbe good shooters. For $150 you could gest a Rough Riger 22 revolver. If money is an issue buy a rough rider. It costs more for the gun. But you will save a lot on ammo very quickly. .25 auto runs from $10 to $20 for 50 rounds. That is almost 10 times the cost of 22lr.
Romans 1:16 I am not ashamed of the gospel, because it is the power of God for the salvation of everyone who believes: first for the Jew, then for the Gentile.