I don't trust a lot of new stuff such as water based primers or gloss - give me smelly oil based paints any day. To get overpaintable silicone you lose some of the most precious properties of silicone ie that nothing sticks to it is good! Generally silicone is for bathrooms/showers/kitchens not usually used with paints, use acrylics for frame/gap sealing where paints are used. Of course the manufacturers will try any 'new' idea to help sales, whether or not it is actually better.
I did check up on a few things and my previous message was pretty near to the mark ie
- Big brands earn big bucks (but higher price doesn't always guarantee better product)
- Be wary of cheap own labels e.g DIy shed labels - they buy by price, some grades can be artifically extended with white spirit made cheaper but evaporates over time leaving a shrunk harder seal that will not cope with any movement!! That said, some own labels may also be the very materials commanding 5-100% more in other brands!!
- Best bet is to avoid DIY sheds, they do not really play for good materials and repeat business, on the other hand buy brands from builders merchants who need plumbers to keep coming back.
Everbuild, Vallance (own by Bostik), Bond-it, Adshead Ratcliffe, Wurth are all good brands. Unibond are owned by Henkel who also own Solvite, Elch and Loctite are also good but you tend to pay a premium