In many cases it's not a great idea because it makes it look like your product is a lot more expensive than it is, and the customer has no idea there's a way to get a better price. It happened to me with Youtube Premium, I thought it was expensive at €16 (instead of €12 in reality), and only found out by chance it was the iOS pricing.
Wouldn't you look for more information outside the appstore before you buy into a subscription? I mean if you do that you should stumble upon the actual price and maybe an explanation for the higher price in the appstore.
It's less a problem for Basecamp than for Spotify, who have a more mainstream product and audience.
> 3.1.3(b) [...] You must not directly or indirectly target iOS users to use a purchasing method other than in-app purchase, and your general communications about other purchasing methods must not discourage use of in-app purchase.
from https://developer.apple.com/app-store/review/guidelines/#mul...