Here's and important detail regarding the climbing technique in the real-world Citation Mustang. Same goes for the VSKYLABS 510X-VLJ:
The common practice is to initiate climbing, in the real-world Mustang, as well as in the VSKYLABS 510X-VLJ is to initiate the climb at speed of 170 knots until intercepting Mach 0.45. Then proceeding the climb at Mach 0.45.
To note that the climbing performance in the Mustang is highly affected from aircraft weight and ambient temperature (the Mustang is not an overpowered aircraft...), and at FL330 to FL400 the acceptable climbing rate should be approximately 700 feet/minute (again, depending on weight and temps).