I have been using the rubber keeper for 15 years. I got it from Canada, at the time it cost me about $80 -100 nzd from this website: http://manymoonsalternatives.com/ it arrived on time, and I never had a problem with the service. I have bought a second one after 10 years, and only cos I was stupid enough to drop my other in the toilet...
I've never used a silicon one and went for the rubber because it seemed more 'natural' and biodegradeable in the end. Obviously I'm not allergic to rubber. The cup has been fantastic, I have leaked once or twice after several hours, but I see my cup has a 13ml capacity compared to 20+ for others [thanks wikipedia]! My boyfriend has even managed to have sex with me with my keeper in and it never leaked then!
I used to have terrible problems with tamps - causing heavier, longer bleeding, cramps and that was when I could get them in! I am sure that whilst there may be a link to endometriosis, I would rather risk that than a monthly injection of man-made fibres and chemicals which could lead to infertility / cervical cancer [we all know the links about chemicals and cancer right? So why practically main line them directly into your body?] I would also say that my sister has endo and used tamps, while I used the keeper and don't! Also when you think of how much I spent on a keeper, it pretty much paid for itself in one year of not buying tamps so it was a bargain when you think how long it took before I bought another [that second one cost me £20].
I bought the smaller size when I started using in my 20's and when I got the new one, I went for the same size. I'm over 30, never had kids and never had a problem inserting / getting the cup to open and as I said I'm sure the couple of leaks were capacity related. I think that with regards to there being only 2 sizes for over a certain age / childbirth that if you are a small person like me you might want to go for the smaller size if you are over 30 and have trouble with the larger one opening after insertion, go for one that has a money-back guarantee.
I checked out a Diva Cup that my colleague got after I recommended the cup to her. I did not like it much, it seemed much stiffer than my keeper...which might have something to do with another users cracking?
I've never boiled my keeper, but wash it in vinegar and hot water or mild anti-bac soap. I would not use tea tree oil as oils act like solvents and can degrade the cup [unless you make a spray of a couple of drops of oil mix with vodka and then add water - the vodka disperses the oil properly]. I've never had trouble with infections or smells coming from the cup! However it does change colour over time and I could see why people might choose silicon over rubber as it looks 'cleaner'.
I have experienced a 'pressure' on my bladder but nothing serious which I don't find a deterrent from using the cup.
I am thinking of trying the lunette as a back-up, and also I want to get one for my step-neice when she starts her periods. I have recommended the cups to all my friends and they have all got them and loved them!