What does JustCall do well? It is one of the only VOIP products that will allow you to get all the features with only 1 seat. Direct integration with ActiveCampaign as well as Integration with Zapier. The development and support team are ON THE BALL. It is very easy to get started and use on a daily basis. The service allows you to replace your current SMS provider. They have webhook enabled messaging as well as SMS Campaigns for the same cost.
What does JustCall not do well? There are glitches in the MacOS and iOS apps that make certain things irritating. The "phonebook/address book" doesn't make it easy to store numbers. The caller ID has issues sometimes and the refresh rate on the application stinks so I'm always having to manually refresh to get text messages updated. MacOS app needs a refresh as welll.
What do you wish you had known about JustCall before using? While the features are excellent, I wish I'd known how crummy the various apps are. Once they get these redesigned, this will officially be a killer app.
Have you used a competitor to JustCall? If so, how does it compare? Cheaper than RingCentral as well as better features. It allows you to do very complex stuff with out the big pricetag.