Hi Dave, I'm another one of the sigrok devs. It's great to see you consider using our project!
And as a result the app (whilst being open source) may not be free on the various platform, but 121GW purchasers will get a voucher code for it.
I'm not totally familiar with all the details of the GPL but there are two questions popping up in my head:
1) Is it legal to charge money for apps that make use of GPL components?
2) The iTunes TOS and the GPL are inherently incompatible:
http://www.fsf.org/blogs/licensing/more-about-the-app-store-gpl-enforcement (alm mentioned this, too). This could mean that the iOS app would have to be built without libsigrok in order to be "clean".
We have not looked into the work required to do this, and we are presuming it will not be trivial. So please don't just answer Yes because it sounds cool, only answer yes if you think it will be really beneficial.
From my point of view it would be beneficial for sure because it greatly increases your potential user base if you support more multimeters. Depending on the architecture of the app, using the libsigrok API may be trivial or non-trivial, it all depends.
I'm not voting, btw.
There appears to be overlap with sigrok-meter, but that does not seem to be actively developed (last substantial commit was in 2015). Having a feature-complete GUI for the DMMs supported by Sigrok would certainly be welcome.
While sigrok-meter isn't full-featured like biot already wrote, it is quite useful as it is. Of course it would be nice to see new features added but unfortunately, we don't have enough developers to make it happen.
Either way we will make sure the 121GW is supported in the Sigrok library.
I like the sound of that!
I think the first step is to provide an easy to use API that can be called from C or C++ or whatever language, and then think about further abstraction. I believe that if your API is good enough, there will people writing Sigrok stub library for you for free.
The only reason I can see for doing this is the iTunes<->GPL issue. However, that would require both apps to run at the same time and sounds difficult to pull off in a cross-platform manner. With that, I don't see this happening. For all other platforms, building on top of libsigrok is a non-issue.