The regressions are in that it is much slower and wastes screen real estate. 90% of the window size is for faux buttons that have zero purpose for anyone who doesn't use a touch screen on their Windows computer (ie. at least 99% of the Windows users) and the 10% that remains uses oversized elements with wasteful padding.

Here is what i use as a calculator on Windows: http://runtimeterror.com/tools/calc/calc.hta.txt

It looks like this: https://i.imgur.com/eWZfcXB.png

and not only is much faster to open than Windows Calculator (ironic, considering it loads an entire browser engine) but also more compact and doesn't waste any screen space (100% of its window is dedicated to its actual functionality instead of being an obsolete skeuomorphism that was originally made to help people associate desktop calculators with the virtual desktop metaphor used on the Macintosh back in 1984 when actual physical desktop calculators could be found everywhere).