They are not exactly pro-grade. While they have a lot of features and some neat technology, in the end, they are a slightly overpriced, mediocre brand. They don't sound bad, but they are made to meet a dollar amount.
The St James is really no more than an amp without a power transformer. They use a switch-mode power supply instead of an analog Iron transformer. This cuts a lot of weight but adds a part that is truly non-user serviceable. When the power supply goes tits up, the amp is done. And as with most things modern, when a part breaks, you don't fix it, you replace it, or the whole product... I don't see the value in an amp that weighs two pounds less but has an Achille's heel.
Now if that technology appeals to you, that is great, all I am saying is that I don't see much value in a $1,200 amp that has pretty much all the same features of similarly priced units, but is up to 47% lighter. For $100-$200 more you can get a Revv D20/G20 and while not 50 watts, they have a real IR loader built-in and are another level up from Blackstar. I would go Revv D20 or G20 all day every day over anything Blackstar. The Two Notes IR's alone make it worth the cost.