That device in the OP is an adapter, not a converter - basically it's just an HD/DB15 breakout, it doesn't convert a VGA signal into a CGA one.
a CRT is well wort the effort IMO, but if yours needs 15kHz/CGA, feeding it VGA through whatever plug or wires won't do you much good.
crt_emudriver is a great option. If your laptop has a Radeon card and a VGA out, there's a good chance crt_emudriver will work on it, otherwise look into crt_emudriver on a coventional PC with a compatible Radeon card.