Hello Anton, it's nice that we can discuss things here. I completely understand if you make your engine private. As far as Spectral and Dark Sister are concerned: A friend of mine wrote to me that he had searched in vain for Spectral 5.20 on the Internet. Because I couldn't help him (I don't need this engine myself because I only test on PlayChess) I wrote to you.
I'm a little confused when you say that Dark Sister and Spectral are now private. There is someone on PlayChess (I don't want to write his real name here), but he has many computers (he has at least 4 accounts on PlayChess alone).
He recently played with Spectral 5.20, and is currently playing live with his accounts with Dark Sister 8.21:
His accounts are Theorymaster, Brainlearn, Chiliklaus and Mtbms. If you don't share your engine, then I have to assume that this player got the engine as your beta tester? The same guy also wanted my private engine Sun 4.1. I'm sorry but if he acts as your beta tester then he won't get my engine. Besides, I don't trust him!! Just because I didn't want to give him my engine, he insulted me in the chat on PlayChess yesterday by calling me a liar and a cheat. As I said, I just told him that I don't share my engine with him, nothing more and nothing less. He even called me by phone and asked for my engine. Nobody needs people who insult others just because they don't get something they would like. If he is your tester, then I hope you have fun with him.