It's not exactly comfortable, but it works!
Circumstances forced my hand — I have to file my own tax return for last year. Because I have a Data Box, I must do it electronically. Filing a tax return isn't particularly complicated: add up a few numbers, put them in the right boxes, done.
What I was a bit nervous about was the tax portal, ADISEPO. It doesn't look modern and doesn't behave that way either. Definitely not in Safari. I navigated there from the Citizen's Portal. Started filling in everything needed and got stuck at uploading documents. It's a shame the actual filing isn't more like a wizard that guides you through each step, because a lot of text is in small print and the last thing you want is to make a mistake on a tax return. Not to mention that if you have income from more than one employer (you changed jobs), you must attach only one appendix — which places additional "technical" demands on the user/taxpayer.
In the end I managed to upload and submit everything successfully. I've filed — but even after more than a month I haven't received any confirmation along the lines of "it's fine, you're sorted for this year." And yet all of this could be so nicely automated…
Hopefully we'll get there — the Moje daně (My Taxes) portal is on its way… as soon as the tender documentation gets revised, that is. From the previous tender Huawei was excluded (based on a warning issued by NÚKIB), and after the company's protests the tender was cancelled.