I don't see any meaningful reason to not go with tempered glass, if you've decided to have a side window. The acrylic windows on the Fractal cases are just like Phanteks, VERY prone to scratches. Tempered glass is also much better at absorbing high pitch noises coming from graphics card etc.
The choice is personal ,whether you want tempered glass or not , there are pro's and con's to all choices . I'm not a fan of the 4 fixing thumb screws to hold a side panel on , i much prefer hinged door approach but that's just me
TG all the way - even just for looks alone.
My cat jumps/climbs/claws her way to the top of my PC and not a mark to be seen. I'd dare say if it was acrylic I'd have a cloudy scratched up mess.
I have the acrylic define C and the window is its weakest link. It got scratched almost immediately, it doesn't dampen noise, I had to clamp it down better for it not to resonate, it's bit of a dust magnet, list goes on and on...
Go TG or solid panel, acrylic is absolute trash. Good choice. Though Meshify has slightly better airflow.