Some manufacturers rely on outside suppliers for the membranes used in their vacuum cups.
At Millipore, we use our own membranes. It's one way that we ensure the quality our products. After all, you can't claim to have the best filter device if you don't have the best filter. Attach a Steriflip filter unit to a 50 mL centrifuge tube containing your sample, flip it over, and apply vacuum. No more sample transfers.