TSO should be clipped with Heatseaker Missiles and not used for it.I initially took this guide down, as I posted it like 20 minutes after the guide you're referring to (didn't want to step on any toes).
Here's my stance: Fusion Missile, imo, is NOT worth casting without using Thermal Sensor Override (TSO) before, unless you're AOEing. Now, if you're using Fusion Missile with TSO, it's viable. However, I tend to save TSO for Heatseeker Missiles in my rotation. Heatseeker Missiles, with 5 stacks of Heat Signature, seems a better use of TSO.
That other fella had a chart with some of the math, so maybe he's right. However, I see bigger numbers with a Heatseeker Missile crit than than damage + DoT from Fusion Missile all the time.
Fusion Missile Tooltip: 971-1065 kinetic damage, plus 1240 elemental damage over 6 seconds.
Heatseeker Missile Tooltip: 1483-1570 kinetic damage. Increased by %5 per Heat Signature.
Now, by those numbers, it certainly looks viable. However, the only way to make it useful is when paired with Thermal Sensor Override. For more than one mob, the damage output of Fusion Missile increases exponentially beyond your other abilities, and should be used if there's only even one additional target in range. (Though, watch aggro and breaking CCs).
For single targets, I don't. You can, especially if you pop Power Surge to make it instant cast, and you'll do fine. Just NEVER use it for single target without TSO.