Same here I used Handcent forever and now Textra always on my HTC M9. I love it! But now I am kind of liking the stock one on this Edge. I love how I change a theme and it changes and my keyboard changes. But my main thing with Textra and Handcent was the colored envelopes at the top for people and a special notification tone for each person which I just was told I can do on the stock app here. Well my friend with a Note 5 showed me where to go to set up a special notification for people and it didn't work I only hear the standard texting one I thought under contacts. I could set up a ringtone and a notification tone so I am going to use this for a bit and see how I like it even though I did download Textra and I may use it now. But I set my friends texting tone to something and it didn't work so maybe it can't be done in the stock app. I like how you can set a favorite at the top if the stock texting app too.
Edit: Turns out it worked I went under contacts and not only can you set a ringtone you can set a notification tone for someone. I just didn't save it and now it works. But I have my own ringtones and notfications in a folder on my old sd card I am hoping they show up when I go to select under contacts. My old phone would show me different things android and zedge and something else. But i had to reset my M9 and it didn't show my own ones anymore.