Anything that has a learning curve and involves equipment is made considerably more frustrating and difficult to learn when the equipment being used is of insufficient quality.
If the end of the tube that goes against your pelvis is sharp, it obviously wasn’t designed well.
I know you’ve already bought 2 pumps, but I strongly suggest buying a good quality cylinder by itself, one with a good rounded plastic edge that can be used both with and without the silicone bumpers, and a dedicated Mitty vac pump with a gauge and a vacuum hose that connects to the cylinder with a plastic quick-disconnect connector with an o-ring.
Or, you can get the leluv smart pump PLUS the adapter that allows you to connect it with any separate tube that has the quick disconnect.
But it is important to have a good quality tube. There are no good quality tubes that have a built in pump.
Once you have good quality equipment that you trust, you know that any issues you’re having are due to your technique and the way you use the equipment. Otherwise you’ll never be sure whether you’re doing it wrong and need to change, or you’re simply being failed by your deficient equipment.
STARTING: BPEL: 5.9in EG: 5.0in
2018: BPEL: 6.7in EG: 5.3in
NOW (start 1/2024): BPEL: 6.9in. EG: 5.4in