Hi, I'm zone 4, also. I've not used JBP before, but here's my take on it anyway. Check the tag that they've got there. Some places will sell stuff that's zone 5 -- even though it's not for our zone.

Second, how much is it and are you willing to take a chance? I've had conflicting reports on plants like Harry Lauder's Walking Stick, (reported as zone 4 and zone 5) but if I like it well enough I'm going to try one.

If you've got a good micro-climate going, I'd take the plunge and do it. The best micro-climate spot I'd ever seen had brick patios around it and a brick wall behind -- very warm all year.

Just ten seconds on google: looks like some do rate it for zone 4 and it's been having pest problems.

Good luck!

Here is a link that might be useful: Japanese Black Pine - Virginia Extension

HI,
I have three BJ pines. Bought them at Lowe's 6 years ago. They were about 2 feet tall. They are now well over 20 feet tall, even bent over as they are.
I just love their bent, distorted limbs, created by the weather. All forms of weather affect their growth and appearance and that is what they are loved for - their distorted trunks and limbs.
Here in my part of Oklahoma, we get below zero temps day and night in winter that can last for a week or more, with blasting northern winds. The cold doesn't seem to bother them, nor the winter precips, but heavy accumulations of snow and ice doubles them over, often all the way to the ground. A few small branches snap off, but the main trunks are flexible enough that they don't break. After the snow and ice melts, they never stand completely straight again.
They also bend with the prevailing winds that blow into the state year round - southwesterly in the summer and northwesterly in winter.
The only thing that I have seen that affects them is drought. We had a severe drought for two years straight and in spite of my watering them, most of their needles turned brown. I thought I would lose them, but they recovered once the drought ended.
Have not had any pests or disease - knock on wood.

Hope this helps you in some way.

~ sweetannie4u