It has great red sensitivity and mild (at best) ir sensitivity. With a red filter 25 or 29 it produces wonderfull results. The portraits of me on my web site (http://www.mrcallow.com*) were shot using SFX and a red #25 filter. On the plus side it is 'ir like' when used with a strong red filter and has better (as in smaller) grain than kodak's HIE, and is much faster than Mako (my spelling).
*To see all of the portraits keep hitting links. the portaraits change as you click. Don't use the back button.