I use one for years and I'm ver satisfied with it.
There are cheaper options from other brands with mics that looks a lot like the ATM35.
Also AKG and Shure clip ons are available.
For the Bass-side I use a Shure SM57
Have a JTS clip on but don't use it any more. Sounded very " un-warm' if you know what I mean...also readily picked up accordion noises like buttons 'clack' and bellows breathing and any bumps or scrapes on clothing or mic stands etc. I play in all electric bands and it was difficult to control for feedback ' edginess' and I became distracted with it. Now have all accordions internally miked..WAY better !
EQ EQ EQ EQ. You can never have enough equalization. Don't believe me? Check out Paul Daigle's set up. He's playing through an amp with a wireless system, but he's also got a 31 band equalizer that he uses before he goes into the amp.
Tuning a sound system to a particular room is extremely important and often overlooked way to prevent feedback issues. I've played with people over the years that say they totally zeroed in their system (in their garage) and know that's the best way to set the EQ everywhere, even though they were constantly having feedback issues because the venue we were playing in was 10 times the size of their garage.
The microphone you're using shouldn't be having a lot of feedback issues unless the wire is compromised in some way or you're playing directly in front of a monitor that is either poorly equalized or set at an ungodly high level. If you've gotta wear earplugs and still think its too loud, its time to get a new drummer or fire the guitar player.
I have an external clip on that I used to use a long time ago. It is a Shure R-65.
It was OK, I suppose, but I switched to all internal mics and now feedback is almost nonexistent. It does change the sound somewhat however. It ends up being more of a Zydeco sound than a Cajun sound, but that's OK with me. Anything to get rid of feedback is worth it.