I like the collar, cutter and templet.
But that requires the utmost attention and control.
It can be mastered, however, with good cutters and an afternoon of waste. An edge guide
and straight cutter is also an option.
But equally difficult to control and stop on a dime.
Stick has an important point with slotters. Straight cutters are not the tools of choice for shallow slots down & cross grain, slotters are a lot better. But you still have a difficult control problem, no matter how you employ the cutter.
The least risky method with the most control transfers the skill and experience issues to one of templet and set up. 2 templets, one for the inside (for collars), a square or rectangle, and one for the outside (a window templet to trap the collar pathway), is nearly risk free.
But making, testing, and fixturing the templets will take some serious time. Nuthin's easy (done well), but you see it all the time.