If I may, I'd like to offer some first-hand information as an early operator of the G150.
Yes, FSI DFW is the only 142 trainer for the type with two sims available.
The slat system of the G150 is greatly improved over the G100/IA-1125, using different flex shafts and improved actuators that are similar to the G200. The improved system has been very reliable overall and is not a focal point failure item on Gulfstream's PS radar.
The Collins avionics platform of the G150 is by far the best application of the system in any PL21 equipped aircraft. And, yes...better than the CL30. The ADI display is edge to edge...unlike the CL30, it has more "standard" features, and includes the side mounted CCD's of the Big G's. There's a lot of available information that can be accessed multiple ways for convenience and redundancy.
However "old school" they may be, the boot deice system is very effective and does not rob the engines of power in any way. In fact, the system is rarely used due to the design of the airfoil. Like the G100/IA-1125/GALX, the wing just doesn't accrete ice like other airframes can. One draw back of the grey colored boot material on the G150, and later G200's, is that it's more difficult to tell when there is a little ice accretion versus the black boot material.
While the G150 will not out climb a LR60...It will go farther, faster, with a shorter runway requirement than the LR60, with nearly identical SFC. At mid-weight and standard temps the G150 will cruise comfortably at FL450, .78-.80M, on 1150-1200 lbs/hr. fuel burn. At FL400-410 following a MGW departure with a max cruise power setting it will accelerate to .78-.80 initially, and continue to accelerate to .84-.85 as fuel burns off. If range is the goal, maintaining .76-.78 and step climbing to FL430-450 yields the best NM/LB in my experience.
It's control continuity isn't as nice as a Falcon, or even a KA200 for that matter. Yes it's a little heavy in feel, has a unique un-stick quality at rotation...but it's not that bad overall. It's ground steering is very nice, with 7 degree L/R ability through the pedals. It's wheel brakes are very strong and it's easy to apply them smoothly. The air-brake system is redesigned using 8 total panels. In flight they may be deployed as one on each wing, or two on each wing. Ground ABs deploy all 8 panels when WOW during landing or RTO.
My only real gripe about the airplane is that it has an aft CG. Due diligence must be exercised when loading max fuel to remain inside the envelope. Most all airplanes have compromises, but in its category...the G150 performs most all missions very well.