Yo, congrats on the R5II! Chicago weddings are a total marathon so I totally get why you need the extra juice. Ive been digging into the specs on these new grips and honestly, the price jump for the fan is pretty wild. Heres what I would suggest you consider before dropping that cash:

• The Canon BG-R20 Battery Grip for EOS R5 Mark II is your safest bet for wedding work. It keeps the weather sealing intact which is huge if you get caught in a random lakefront downpour. I wouldnt really trust a third party one with that body just yet tbh.
• About that Canon CF-R20EP Cooling Fan Grip for EOS R5 Mark II... its cool but unless you are pushing 8K 60p or long 4K HQ clips in 90-degree humidity, you probably dont need it. It actually draws power to run the fan system, which is kinda annoying if you are strictly trying to maximize shooting time.
• Make sure you are using the new Canon LP-E6P High-Output Lithium-Ion Battery packs. The older NH versions work but you lose the top-tier video modes and some burst speed anyway.
• I havent seen a reliable Neewer Vertical Battery Grip for Canon EOS R5 for this specific Mark II model yet. Since the new body uses a different communication interface, I would be really cautious about using a knock-off this early... you dont want a weird power surge messing with your new sensor. Just bite the bullet on the Canon one for peace of mind.

I've been really happy with the Canon BG-R20 Battery Grip. I'm pretty cautious about my gear and once had a cheap grip fail during a wedding, so I strictly use OEM now for the safety. The Canon CF-R20EP Cooling Fan Battery Grip is technical overkill for stills tho, unless you're doing long 8K clips. TL;DR: Stick to the Canon BG-R20 Battery Grip for reliability and weather sealing.

Regarding what #2 said about "Ive been really happy with the Canon BG-R20..." - i definitely agree that sticking to the brand name stuff is usually the safest bet when youre dealing with high-end bodies like the R5II. You really gotta be careful with how those contacts align because one tiny short and your whole day is toast. I always tell people to make sure they test everything for a week before a big gig like a wedding. Honestly weddings are just absolute chaos anyway, right? Like you think youre prepared for every technical hurdle and then something totally out of left field happens that has nothing to do with your gear. Man, this whole conversation about wedding prep reminds me of this one gig I did a few years back. I had all my gear double checked, but the venue was this old converted barn out in the sticks. About an hour before the ceremony, the entire power grid for the property just blinked out. The wedding coordinator was totally freaking out, the brides mother was crying, and i was just standing there with my camera thinking about how the light was actually getting better because of the storm clouds. We ended up having to use car headlights to illuminate the cake cutting because it was pitch black inside. It was such a mess and honestly nobody even cared about the photos for like three hours because they were too busy trying to find a generator for the DJ so they could keep the music going. It just goes to show you can plan everything perfectly and still end up in a weird spot... anyway, weddings are wild. But yeah, definitely be careful with whatever you choose.