For a keychain light? Absolutely!
For EDC, sure, get a jack-of-all-trades (and master of none) flashlight what all kinds of modes, no worries. For a simple keychain light? On/off is usually plenty. If you want moonlight in the middle of the night, by the time you flip through all the other modes, you’re already night-blind.
I have so many “special-purpose” lights that are 1-mode only. The most high-rel lights are 1-mode only. 7135-based lights have parallellism in their favor (no µC to go mental on you), and simple resistored-DD lights are even simpler at the expense of current-regulation (ie, light drops off as the cell is discharged).
I only use “modes” when I’ve got other lights to back me up. That light I can afford to be a JOAT as far as brightness, but the beam is still the exact same across all modes.
That’s why for most “normal people”, I’ll recommend a zoomie, even though I generally dislike ’em (except if the moveble head were welded into a permaflood position). But for muggles, yeah, zoomies give ’em that range from flood to batsignal, dim to bright.
But for those who can’t handle even that, who view those with disdain, who want a simple on/off just like their plastic-tube glass-bulb 2×D drugstore special, hey, give ’em what they want.
I know someone who doesn’t seem to remember that lights can have modes, and who’ll leave the light on whatever mode it was last in, and doesn’t/can’t figure that it can be changed brighter/dimmer. People like that, they’ll be disgruntled that the damned light is so dim and good for $#$#&! (Nevermind that it’s stuck in moonlight mode.)
Let’s face it. We’re not normal people. 
