Hoya Sq100 Filters

[C4RBON]

I have Breakthrough 77mm ND filters for my EF lenses (I've managed to buy mostly lenses with 77mm filter threads). But I'm anticipating getting RF lenses with larger filters (once I migrate to an RF mount body). I'd like to move to 100mm square format filters, since they can be adapted to various lenses. I've also started using 100x150mm graduated ND filters for landscape work. I have the Breakthrough filter holder and a 2-stop graduated ND filter.

I'm happy with the quality of Breakthrough filters, but I'm growing frustrated with the 100mm square ND filters being perpetually out of stock. I'm starting to look for alternatives.

Does anyone have alternate suggestions for 100mm square filters with equal optical quality (sharpness and color neutrality) and durability?

Jason

Edit: I'll take a look at Kase; I hadn't heard of them before.