I picked up the BookBook vol. 2 for iPad Pro (Link:
https://www.twelvesouth.com/products/bookbook-vol-2-for-ipad-pro?variant=19242839801913#shopify-section-bookbook-vol-2-for-ipad-pro) and I absolutely love it.
I have a holder like this,
9 Pack Pen Loop Holder, Volin Crik Self-Adhesive Pen Holder Pencil Elastic Loop Designed for Notebooks, Journals,Calendars (Black 9pcs) https://www.amazon.com/dp/B078W67NRQ/ref=cm_sw_r_cp_api_i_VXVkDb163RRAV
But will likely get this,
Erin Condren Metallic Pen Holder Trio (Acc-PENHOLM) https://www.amazon.com/dp/B01GJSMIQU/ref=cm_sw_r_cp_api_i_TWVkDb2MR755Y,
Because SPARKLE! 
I should point out that it’s certainly quite possible to leave the pen attached (and thereby charged, in the BookBook, however when I’m using it throughout the day, I’m worried I will lose it so I like adding pen loops to things. Also, the pen perfectly fits in the middle fold so when I close it it use the BookBook in any configuration, no issue! Was rather pleased with myself for quickly figuring this out. 
I’ve had a few Twelve South products with rather mixed impressions.
For example, the AirPods holder felt cheap and I gave that away immediately. F- on this one.
I’m likely getting one by Story Leather because their leather products are awesome, you can do custom colors for leather & monogramming on everything and they are very reasonable.
https://www.storyleather.com/airpods-leather-case-nutmeg.html
Only annoying issue is that shipping for custom is like 45-60 days. But my butter soft taupe leather custom key fob holder for my car with gold accents and monogramming makes me smile every day so it was worth it!
Back to Twelve South.
I also have their CaddySack for cables. This works well functionally (though I outgrew it’s storage quickly), but the leather is crap. Honestly, I thought it was pleather. So that’s disappointing. C+ on this one.
I have the iPhone charging frame (Power Pic) and that’s cute,
My husband gifted us each one for Christmas and we surprise each other with new pics randomly. So A+ on that one.
Back to the BookBook v2
A++ rating!
Great implementation on this one. Easy to put the iPad Pro in it (I have the latest one), the various angles of use work well, propped up like a tablet or watching a show, and the leather is beautiful!
Currently reading outside and listening to a Focused podcast episode (yes, I get the irony here ) with the iPad and BookBook and couldn’t be happier.
