abraham Marte was the guy getting the armless triangle choke, but I think he used his arm to filled the space, so it wasnt really an armless triangle.
Now, to op, you wont be putting anyone to sleep if you triangle your legs around your opponents head, but, its a pretty legit technique, specially to transition to an armcrush, but you have to do a couple of things, if you stay square and just squeeze, that shit is going to give your partner some nasty cauliflower ears, but wont stop him escaping through the back door, nor much pressure is in it. Now, if you turn the corner 90 degrees, and do ryan's hall stomp and curl (well not so much the curl motion) motion while grabbing your shin, the pressure is INSANE, most people will tap in the gym, which sucks because I dont think people will tap in competition, but your aim should be to get to the armcrush, the pressure is enough to make them think on whatever but protecting his arm, so you go for the triangle, start "squeezing" as soon as you see a gap, you go for then underhook and armcrush, its basically exactly the same thing as a regular ryangle but with the arm out. It an awful awful position to be in it.