What do you think about MacEggs.com ?
Never heard of it until you mentioned it. They seem to be trying to capitalize on comments about Apple developer platforms that are popular on social media right now.
All I can tell you is to make sure to do good research before entering into any legal agreement. Make sure you know what your rights and responsibilities are. Make sure you know who, specifically, you are entering into an agreement with. Do they have a good reputation? What other apps are using them? How does the licensing work? Who, ultimately, has control over your software and your customers? What sort of infrastructure will you need?
Pay particular attention to your responsibilities for sales tax/VAT, privacy regulations, and consumer law. In many jurisdictions, these laws are applicable based on where the customer is located, not where the vendor is located. And who are you, specifically, in that relationship? Are you really the vendor? Or are you, as a developer, something else in some kind of grey area in between?
If you use Apple, then you have a lot of institutional support and legal recognition. By that I mean you can tell your accountant, your lawyer, and you government tax agency that your business is selling software through Apple's App Stores and they will understand and know how to deal with it. If you do something else, then make sure to consult with your accountant and lawyer first so that they know what you are doing and can tell you exactly how you need to manage the taxation and legal issues.