Oh, yes, that's the workaround for any triggering system. The thing is, it's a PITA when you have to put the meter in one hand, and use the Tx unit in the other--particularly if the Tx is attached to your camera hotshoe at the time. At least the ST-E3-RT can be used in-hand.
The Yongnuo RF-603s are super-obnoxious this way (which is why we keep hearing a Mk II version will be coming out). The 603s have this neat "feature" where they auto-sense if they're supposed to be a Tx or Rx unit. Trouble is, it does this by using one of the TTL pin signals. If it's in-hand, it can't sense the TTL signal, so it never goes into Tx mode, and stubbornly stays in Rx mode. And you can't use it to test fire. So it has to be on the camera to test fire. [facehands]. If the camera's on the tripod, it's hard as a single person to simultaneously hold the meter where you need to and hit the test button the transmitter. Unless you're Plastic Man.
This same issue also means that the triggers don't work on Sony, Olympus, Panasonic, or Pentax hotshoes, even though they're ostensibly "manual-only" triggers, which theoretically
should work. Using a Tx/Rx switch (like Cactus does) doesn't seem so dumb, now.
It's funny to me that they had the right idea, just too early (i.e., when PocketWizard really was the only game in town), and then they abandon the idea just as it's becoming something more people want. OTOH, they can charge $100 more for a meter with a PW Tx in it; they probably don't make money if Yongnuo makes a $25 unit to go in one of their meters; as we all know that YN isn't exactly the kind of company that pays licenses...
So I guess it makes sense. But you'd think that Canon & Nikon might be happy to make compatible triggers for Sekonic and pay them a licensing fee if they didn't want to open the design of the triggering interface.
Still. Canon logic is not our earth logic.