If that was their intent, then yes, that would be an issue. The key is good UX; don't send the user there without explanation. A well-designed "read this!" screen is key, and even then you will lose some users. It's a trade-off.

Also, I did acknowledge that this approach will turn away "mass market" users, but again, I don't think that those users will ever be Signal's primary user base. Most people are going to use stock apps or whatever is most heavily marketed (read: whoever spends the most dollars on acquiring users). Signal frankly can't afford to buy its way into the mass market. It's a niche app, and it should focus on catering to that niche.