I use a T-SLG (Toodles Scanline Generator). Honestly it's hardware, not software so one of the best things about this is it refeclts on anything shown on screen. So MaLa and any emulator I run on the system will have a consistant look.
Very happy with these, and they give a great effect. Well worth the money if you want a retro look on an LCD.
As Almighty said run at a lower resolution, and be sure to adjust the RGB knobs to really get a good effect. I will confess that out of the box I used these on two machines, a 60 in 1 Jamma board and my MAME system.
The 60 in 1 looked great out of the box, no adjustments needed.
The MAME syustem needed some adjustments to get it to look good, but now it does. Really pronounced effect.