No, INSTEON devices are not as susceptible to line noise as X10. INSTEON messages are broadcast on a different frequency on the powerline and with every device being a repeater the network gets stronger as you add more
According to SH (see quote above) Insteon is not supposed to be affected by line noise If you call tech support some say yes and some say no. I personally have problems from CFL bulbs. I cant get switches 6 feet from each other on the same circuit to link. Also reliability is poor at night when the CFL's are turned on.
I think that they really are affected by noise but SH presumed that they would be immune and found out at a later date that they had similar problems to X-10.
FWIW, there's a huge difference between saying something is "not as susceptible" and saying it is totally immune.
In my experience, Insteon devices are more resilient than x10 in the face of noise for a few reasons, including that each unit is a mesh repeater (making for a stronger overall signal) and that the 2-way signal protocol causes devices to auto-retry signals that don't generate an acknowledgment (may be helpful if the noise is cyclic or intermittent). The mesh repeaters maintain signal strength house-wide and allow Insteon devices to, in effect, out-shout low levels of powerline noise and out-broadcast devices that would totally swallow an x10 signal.
IMHO, compatibility with CFL bulbs really depends on *which* CFLs you use. I've experimented with a few that just killed powerline signals, but have been able to swap them all out for units that peacefully co-exist with my Insteon gear. All my basement, utility room and bathroom light fixtures now use CFLs, none of them isolated by signal filters, and my Insteon reliability is 100%. It just depends on how "automation friendly" the manufacturer designs and builds the bulb's ballast. The same goes for some devices with switching power supplies.
There's really no way to build a device that shares a communications medium that is totally immune from interference, unless you give products the technology to zap noise generators with a surge big enough to kill them dead.
No way. Fortunately, selective device replacement with more compatible CFL or switching power supply units, or isolating the noisy loads using noise filters can normally fix problems without resorting to appliance-on-appliance violence.