I’m interested in a flangeless, direct to concrete installation for windows and doors on my ICF single-family build. What do you think of this detail overall?

It’s apparently both tighter and less thermally bridging. Should I still consider leaving the bucks in place?

Here’s a summary of the comparative infiltration testing: https://www.constructioncanada.net/weatherproofing-icf-walls-lessons-in-resiliency-from-b-c-field-testing/3/

What are the drawbacks of this assembly?
What removable buck materials would you use?

Any and all input is welcome!