Hard to say for sure; the answer depends upon what you are comparing it to. If you are comparing a parabolic with a cool tube there's no question it will spread the light more evenly but without ducted venting and in a tight space the parabolic would also throw a lot more heat. Parabolics work best in a large grow area where an a/c or other external climate control in used but its not clear if a parabolic reflector would outperform say a large angled style hood. Both distribute light better than a bare bulb would and should produce similar yields if given the same wattage, strain, and conditions. Temps in my experience are way more important than reflectivity and wattage governs yields for the most part. Reflectors just help distribute the light evenly; IMO you won't see a huge difference unless it's in conjunction with a lighting upgrade.