How do I download HTML Egg for iPhone and iPad?

The iOS edition is a free download with in-app purchase components.
https://apps.apple.com/us/app/html-egg-2-website-designer/id1450771222?ls=1

Does this app work on both my iPhone and iPad?
Yes, HTML Egg 2 is a universal app and is compatible with both the iPhone and iPad.

Does in-app purchase upgrades unlock features on all devices?
Yes, all in-app purchases are one-time upgrades. This means you are only charged once and there are no recurring charges. You can use unlocked features as many times as you like. Purchases of in-app upgrades unlock features for all your devices.

How do I restore purchases that I already made on a new device?
Use the "Restore" button in the In-App purchase section to restore upgrades for multiple devices, there are no charges to restore upgrades. Please make sure you're logged into the App Store using the same Apple ID as used to make the original purchase.