haven't seen them before, but a short tour around their infra/systems providers isn't particularly exciting - depending on both your threat model and what-you-want in a vendor
some parts/pages do provide some detail in encouraging depth, but I'd have to do a much more full review to give you a good answer
there's been a couple of "where email" threads over the last year, tuta's still one of the top options on that but you can check the threads if you want to see some of the other promising options
curious, that art style in that reply strongly matches the image I saw on this toot drifting by in my timeline earlier