They are different, they both have that over all Mesa tone but I have had them side by side and to be honest I prefer the Grail it's one of my favorite stock modules.
The Grail is closer to a pre 500 era recto and it doesn't have the bad fizz and loose bottom the Tremoverb had.
I have liked Recto's for rhythm but using them for lead never really worked for me, it just sounded bland and generic.
The Grail does a great rhythm and great lead sound.
At least that was my experience.
Cheers