It's a sound strategy, but it is an expensive one. I have tried out Zargrul before and made the mistake of buying my copy. In the end I didn't use it much and ended up selling it for a slight loss, but it took forever to sell! Smart move renting it first to see how it works it works out.
Let me know how Gargug is as an archon, never tried it out. I hope you do well with the strategy, too bad you ended up having to rent an archon just to use what you rented though. That was a pricey mistake! Keep up the good work and good luck!
!BBH
!PIZZA
Yes, it is expensive—and for me personally, it cost a bit more than usual—but its performance is quite impressive, especially when the 'Bloodline Tribute' is active, granting +1 to the stats of all cards sharing that bloodline. Based on my experience so far, I’ve concluded that it is better to rent cards rather than purchasing them outright; this allows you to enjoy them for the entire season while simultaneously putting them through the most thorough testing possible.
I'm the same, always rent before you buy! It's too bad those rentals came out so expensive, but I love Bloodline Tribute! Use it all the time in Water! Some cards I just rent, they are too expensive to buy and the rental comes out so cheap it makes no sense to waste money buying an expensive card. Then when it falls out of Modern into Wild the value usually drops like a rock anyway. I remember Llama and Kitty were worth hundreds of dollars back in the day, now they are cheap!