My experience is different from the OP's using android mobile mode.
Whilst already logged in and using the regular link;
I was redirected to the login page and then, not to the form but to the form menu.
The 2nd link;
weirdly took me to;
"404 Page Not Found" whether logged in or not?
I accept that I may have been directed to login, having been logged in for 30 minutes or so, that's a good thing, right!
Trying again after freshly being logged in I go directly to the form, while the 2nd link still takes me to 404 not found.
Edit: playing around a bit changing http to HTTPS gives
Was your experience @sloz using the giffgaff App?