The parent company of Mentor is Johnson & Johnson (think band-aids). This is a very large and well funded company. All Mentor implants are made in the United States and the company is based in the United States. The silicone that is placed in the implants comes from the same company that also supplies Allergan implants.
Mentor offers a lifetime warranty on all their implants. If you have a leak or break in the implant, Mentor will replace the implant for free and the opposite implant for free also. If a silicone implant ruptures then Mentor will provide funds up to $3,500 to cover the surgery costs (anethesia, facility fee, surgeon's fee). The new silicone implants have been on the market place for 9 years now and the rupture rate is extremely low, around 1-2%. The gel is firm and not liquid, therefore it does not "ooze" out from the implant shell and behaves more like jell-o or a gummy bear. These implants appear to be very safe.
US manufacturers of breast implants like mentor have a very good tack record of producing quality products. Discuss implant choice with your surgeon.
Mentor Siltex Round Cohesive Implants
All of the approved cohesive round silicone implants from Mentor, Inamed and Sientra appear to be similar in overall quality. All breast implants are expected to wear out over time from chronic fatigue (wear and tear) and the silicone gel that is inside the implants can cause an inflammatory reaction in the breast tissue once the outer shell is compromised. Regular exams and MRI scans are recommended for long term surveillance of the silicone implants to help determine when replacement may be necessary.
Mentor silicone breast implants
Mentor, along with Allergan and Sientra, are the 3 approved breast implant manufacturers in the USA. They all make very good implants, but there are subtle differences among their products in shape, feel, firmness, etc.
I have not seen a study about differences in longevity or "quality" among the implant makers. Any silicone implant may leak, that's why periodic exams and MRI are recommended to patients.