They do different things. The XPNR / Leviton 6289 attenuates "out-of-band" noise. That helps with things like arcing brushes in universal motors. The XPNR is designed to pass "in-band" signals. Unfortunately, the high frequency chopper in some CFLs runs around the X10 carrier frequency. That is why they cause so much trouble for X10 signals. See my tutorial on CFLs.
The 6287 is designed to block "in-band" signals, which causes most of the trouble from CFLs. It will also isolate signal suckers. So they are the correct choice for this application. The 6287 is pretty small - about 1.5 inches by 2 inches, and maybe 3/4 inch thick. It fits just fine behind an X10 switch in a deep electrical box. If you don't have room, you can wire it in at the offending light fixture. Just be sure to connect it in series so it blocks any noise from reaching the powerline.
Jeff