What source is JurassiCal derived from?
The source is limestone (naturally mined).
JurassiCal™ is promoted as not having any phosphorus added to it, whereas other products are a 2:1 calcium to phosphorus ratio. Won't those help me maintain the proper ratios better?
No, because herbivorous and carnivorous diets are frequently calcium deficient and phosphorus rich. If you add a calcium supplement that has phosphorus in it to a phosphorus rich food source, like crickets, for instance, you raise calcium, but raise phosphorus at the same time. Thus, you have barely improved the ratio at all.