And I never saw an adapter that went from L5-20R to 5-15P, they always went L5-20R to 5-15R or L5-20R to 5-20P (Sure hope I said that right, getting past my bed time). My knowledge is based on walking techs through setting up devices in server rooms and the like. I'm trying not to break electrical codes too much here at this house, the last house on this property burnt down. Hate to have a repeat. (Hence the fancy power strip, so I feel better at night while I really know it's not really doing anything special).
I completely understand. I don't really see it as much of an issue as the prongs on a 15A and 20A plug are the same material, same thickness, etc. The only difference is the hot/neutral is not parallel to each other. If it were a hazard, you wouldn't be able to plug a 15A appliance into a 20A line, for example. The bulk of the power usage usually comes when you turn a device on (depends on device components). It generally results in a quick power-spike before settling into it's true power usage.
If what you are plugging into can handle that, you have nothing to fear. If you're concerned, use a surge protector (as you have stated you plan to). If the line can't handle it, it will cause the breaker to trip. I believe 15A breakers trip around 12A (80% of rated usage). If your device is a continuous amp usage lower than 12A, there is nothing to fear here.
As for twist-lock connectors, there isn't much difference between them and a normal connector. They are made to not yank out if you kick the cord or if someone trips on it.
If you do decide to do it, I would just look at what your power draw will be across all the devices you intend to use and plan it out accordingly. Possibly put the device that has the 20A twist-lock onto a different circuit that doesn't have anything else on it.
