A simple solution! I love seeing peoples different approaches to cruise control. Some controllers do have this feature built-in though and you can "program" them by holding the throttle a few seconds after connecting a certain pin (I think) on controller. I'm not sure how practical the controller approach would be though on the road, and can see why people are coming up with their own switches and other solutions.
I wonder if the manufacturers of these throttles will have noticed this and will bring out a new version of the throttle which has a way of disabling the spring-loaded "pull back".
I noticed the Speedict also has a 6km/h "start up" button feature.. I think this is designed to comply with EU law to allow bikes to be pushed under power up hills? I'm wondering if it might be possible to fit that button and reset the speed higher so it becomes a cruise control, assuming it's a button switch and not a button you have to keep pressed.
Many of the commonly available controllers have a built-in cruise control function, but finding detailed information on how to make it work well isn't easy. The Xiechang (Keywin, e-crazyman, so called "infineon", some Crystalyte, Lyenetc, etc) range of controllers (all basically the same internally, pretty common, reasonably cheap and very easily programmed with a PC) have several cruise control options and these have been pretty well documented on ES. The Wuxi Xichen Micro-Electronic Co range of controllers (KU series, Greentime, Hua Tong, etc etc, again all pretty much identical internally) also seem to have cruise control, but as we haven't been able to crack the programming method we have no way of knowing for sure what the seller or middleman has programmed the cruise settings for.
The Xiechang controllers can have either autocruise, where holding the throttle at one position for a set (programmable) time period activates speed hold, or they can have button activated cruise. They also have LED drive outputs than can display things like cruise setting, speed switch selection etc for a handlebar display. My guess is that the Wuxi Xichen Micro-Electronic Co controllers are probably similar, but without the ability to programme them easily they aren't as versatile.
I found that autocruise, with a long engagement time, was great with a thumb throttle on my recumbent, but that the button activated cruise was a bit awkward to use. Ebrakes were essential to kill the cruise function. My primary concern was being able to ensure that I could kill the power instantly when I used to use this function, as the potential for coming a cropper if the power stayed on even a fraction longer than intended was quite high.
