The Bikebug (Tanaka) engine was 26CCs and the Chicken Power is less than that, if I remember right around 21CCs. I have more experience with the Tanaka motors, but they are very similar and have their place in the history of motorbicycling in the U.S.A. I don't know how popular the Chicken Power was, but Sears did their own branding of of the Bikebug (calling it Free Spirit) and a lot of them were sold. I think the Chicken Power was pretty much mail order.
If you want to go fast, this isn't the way to do it other than down a steep hill. (I blew up one Bug engine that way), but one of these motors on an old skinny tire 3 speed was quite nice. No burnouts and the chances of going uphill without pedaling were slim to none, but there was something nice about pedaling up to speed and then just cruising along on a flat without having to pedal... the engine using very little fuel and making little noise. Being friction drive with the roller disengaged from the front wheel there is no resistance at all and the engine being as light as it is (either one... the bug motor or the chicken power) you hardly notice it being there. On a flat you can cruise all day long with very little pedaling ever needed. Want some exercise, disengage the engine and shut it off with the kill switch. This kind of wimpy little engine has it's place and value, I think. I still have one sitting on a shelf and some extra parts. Maybe one day I'll fix up an old 3 speed English bike like I had as a teenager. In fact I have a Robin Hood bike made in England in very nice condition. I'll set it aside as a future little project, I think.
SB