Like anything else it depends on the one you choose and who your therapist is. But, yes, they can work. I used Talkspace for a little bit. I met the therapist via video chat. After that sessions were over the phone or via instant message. The instant message was nice. I could send a question and even if the therapist couldn’t get to it immediately, within 12 hours I would have a response.
Betterhelp.com seems pretty popular too.
As far as insurance, once again it depends. To make it easy and maybe because my employer doesn’t, or didn’t at the time cover it, I paid out of pocket. This is what Talkspace has to say about insurance: https://help.talkspace.com/hc/en-us/articles/360000286363-Is-Talkspace-covered-by-insurance
At the end of the day, it seems very similar to or the same as having a normal therapist. Instead of going to a building/office, you are online. One key suggestion is, don’t be afraid to change therapists if you don’t like the first one you get.
If you are asking about any type of therapy apps without actual live therapists, that I can’t answer. I’m sure all kinds of apps exist which might claim to help your mood via special sound waves or something. I wouldn’t trust them. The only type of non-therapist therapy app I can recommend would be a meditation app. Any meditation app. Because meditation can also help; sometimes; for some people.