Vacuum Cup vs Silicone Cup

I found using an extender with comfort strap intolerable despite my best efforts. Could only keep it on for a short time.

So I have set up my extender to worth a silicone cup from ebay, the ESL40.…=item337e31f168

In short, it works great. I can extend for hours without a problem. The cup goes on quick and easy. It stays put.

My question is, am I missing out without using a vacuum cup like the vacextender. Does the vacuum cup work better than the silicone cup? I have not used a vacuum cup before and am looking for opinions from people who have used both.