Yes, comparing to Porkbun for .com and .net, it looks like you'd need at least around 10 domains before it became cost effective (the .org price there says it is time limited and I think does not reflect recent .org price increases).

There's also the matter that, ethically, openprovider seems to be heavily focusing on domain name speculators as clients; that may be a business many people would not want to support, and their services for people actually using their domains may be poor.