I feel like the MIS would be very useful for fleets. Its like a budget constellation in terms of missile armament, though the other anti-ship weapons, and ESPECIALLY the cargo capacity, are lacking in comparison. Its a relatively maneuverable missile boat that is cheaper to maintain, buy and crew than the constellation.
Essentially, its a pocket battleship. It has the guns of the big boys (in this case having only a slightly inferior missile load than the constellation, due to its requirement to fire 20 then reload), but defensive assets comparable to fighters. 4 size 2 missiles, and this thing will have its shields down and be considerably damaged, if not destroyed.
These things were built to strike en masse from a distance, unload their first set of missiles, let the reloading mechanism give em 20 more, unload those, then run like hell before the surviving hornets and 300i's get a chance to close. You could potentially halve an enemy strike group with anything short of a corvette before they had time to respond if you had 6 or more MIS in a group.
However, its not perfect, there are drawbacks. a constellation can haul twice as much mass as a MAX, then outfight a MIS, and thats not even considering if it launched its snub fighter to deal even more damage. If you can afford the constellation, get one. If all you've got is 165 dollars, then you will be able to cause more damage with the MIS in a shorter time frame than any thing sold for less than 200 dollars.
regarding the LTI, no. You lose it if you melt it. However, upgrade, you should post that on the RSI forums. A moderator can handle that question better than us.