Pretty much the difference of one opinion vs another.
Having played this in several games involving Infantry, BA, and even a few tanks, it does surprisingly well if you think about your goals and what you're doing. It's a pretty decent bug killer too, and the ERLL is an improvement over the old AC/2 in retaining "token range fire". While the armor isn't the greatest, it's a vast improvement and it has a higher BV than any other Vulcan model I'm familiar with and it's cheaper than the VL-5S, VL-5Sr, VL-6M, VL-6P, and even the VL-6M-UK models.
Not the greatest mech, but honestly what 40 tonner is?