I installed this, only to have it playing tones twice and after a few hours of this I got so annoyed I went back to the old one
Again, with biteSMS (paid version, but the free one should be the same), no issues once I got it dialed in. I have Text Tone in Sounds set to "None." I have ToneFXs New Text Message set to "Silent." Works fine, only one sound (from biteSMS). I have individual tones for each person in my contacts list, and a general tone as well. Bite has a free version, maybe try that and see how it works? I messed around for a few minutes and got it to work.
Anyone else having an issue with the latest ToneFXs version in which the system sounds sound muffled after a certain amount of time?