I have also had some polyspan clones. Uneven texture, thin spots. No way to ever fill that weave. The original Starline was the best but are they in business anymore?
A similar product is Thermalspan. Apply and shrink like polyspan but Thermalspan does not have the "grain" like polyspan. Thermalspan is as strong in the chord-wise direction as span-wise. The weave looks tighter. Like polyspan, it needs to be installed with the proper side up. I doubt if the company that made this product is still around. Since fewer are building these days, and the demand for such items has dropped, no reason to produce it.