If you're comfortable with it, why not.
Here's a newsflash for ya - even if you have a call that is biochemically designed to match your dna with that of a goose's and make you spit down out the end of the insert, not every goose that you blow at is gonna work into your spread...it'S that simple. I consider myself a decent caller, and they don't all come in. That being said, the this call / that call debate should really only come down to what you can comfortably run and get goose vocabulary out of. If you are comfortable running only a SMH, then why not - you will get some birds to commit with it, you fail to get all to commit with it.
I only run one call when I hunt. Because I prefer higher pitch and the option for more volume, I would never run a SMH - that and I simply don't like the sound, response, or fit of that call. My view is simple - if you can run a high call well, you can get it low when needed. If a call has volume, it's there when needed, but you can quiet it down if you have too. If I was going to run only one call from the Foiles stables, it would probably be a HPH. If you're happy with the feel and sound of your SMH, and you're content with your respults, why not.