I think you got this information before, but for the benefit of others -
The b series cameras are designed and calibrated for use at ambient building temperatures. (B for buildings.) The i series cameras are designed for use at much higher industrieal temperatures.
So if you want to use for water damage restoration, home inspection, energy audits and so forth, you want the b series. If you'll be inspecting industrial equipment, electrical junctions and so forth, get the i series.
Buy a b-50 camera through Interlink Supply before the end of this year and you will also get an Extech boroscope free.