Hello, couple days late but, figured I would chime in on this one.
There are several issues that can arise with the mail to link. Its not compatible with every mail client for start, I couldn’t imagine testing a link in every mail client, bet there are a few, most will typically launch the client, typically something gets left out, maybe the subject in Outlook, or Cc in Gmail, Thunder Bird, whatever.
A form sends those variables (message, subject, to) via a POST request, its far safer because its not stored in the browser cache, what if the message contained privileged info, anybody can see it .
The mail to link can also be modified on the client side easily, so anybody could inject javascript in and alter any part of the message, view it, delete it, whatever. Forms ensure the data being sent can be verified by your server before anything happens, check for data integrity, validity, SQL injections, spell their own name wrong ect… where as the links, once that button is clicked, its go baby go, straight to the mail client, no integrity checking.
And lastly, this is my favorite btw, browser bots, more so email harvesting, its an awesome way to get spam, junk, malicious material, and once one gets that address, its for sale. Almost ruin an email account.
Anyways, to each is own, they both work, but thats why forms are the industry standard. Cheers!