I use a Minolta IIIF incident and 10 degree reflective meter with flash testing as well with my RB67 film camera. Of course I've used it for a number of years before cell phones even were invented. I did try a cell phone meter app a few years ago but found it fidgety. I suppose if I worked with it longer, it would get easier. I recommend trying the phone app and see if it works for you. If not, then spend the money and buy a dedicated unit.
Note: I've tried my P&S digital camera to get exposure settings. But it only goes to around f8 or f11 and is fidgety as well. Plus the fractional settings it selects if on auto never match the whole stops on my film camera like a dedicated meter does.
One thing I've started to use my cell phone video program for is to voice record the f stops and shutter speeds and other info when I take film shots. It's easier than pulling out a piece of paper and pen to write down the settings especially when it's freezing cold and you want to get the hell out of there. I can also do a quick clip of the subject at the same time. Then when I get home and warming up with a cup of coffee, I transfer the details to a sheet of paper to keep with my negatives or chromes after they are developed.
Curious, what cell phone apps have you guys tried for a Samsung (Android)? Do they have reflective, incident, spot etc? IS anyone making a display that show something like what an analog shows with all the f settings you can use against the shutter speeds. Now that would be handy on a cell phone.