Just discovered the Boya M-1 lavalier microphone, which is an absolute bargain for smartphone or camera use. It’s about half the price of the Audio Technica ATR3350iS, and less than a third the price of the Rode Smartlav+.
It seems to be more solidly made and better designed than the ATR, with a more positive switch, and a more secure clip. The switch has a simple on-off button: on is for camera use, off is for phone use, so you don’t need a separate TRS-TRRS adapter. It has a really good output level: you could even use it on a table at a pinch, rather than clipping it to clothes. Like the ATR, it has a 6m long lead so your subject doesn’t need to be close to the camera. It comes with a (bulky) foam windshield which fits rather loosely.
The Boya (left) is quite a bit bigger than the little smartLav+, particularly with the windshield attached.
How does it compare? I think the sound is at least as good as the ATR3350 and the level is better. It’s not quite as good as the Rode microphone, though it is louder. Here’s a comparison test (iPhone microphone, smartLav+, ATR3350 and Boya BY-M1). I recorded all of these with the excellent (and free) Rode Reporter app.
The only major issue I had was the notorious iPhone 6/6S headphone socket problem, with the phone refusing to recognise the mic. I solved this by using a piece of tape to stop the metal base of the jack from making contact with the body of the iPhone. You could also use a TRRS extension lead. Also, the foam windshield (which I don’t use indoors) falls off easily.
Being able to use the same microphone for smartphone and camera has got to be useful. It’s so inexpensive that I’d recommend it to any smartphone filmmaker or mobile journalist on a budget, and it would also be good for education use.