I'm taking a thermogen right now that has raspberry ketone included in the mix, but I've also got my diet and exercise way dialed in. It's also got caffeine and some other herbals and as it's a proprietary formula, I have no way of knowing how much RK is actually in there.
My main point being, I'm restricting calories to cut out about 1500 calories per week, lifting heavy 3-4 times a week, and training for a half-marathon 3-4 times per week. I'm also taking care to get at least 7 hours of sleep per night if not more. The pill is just an extra boost thrown on top. I can confidently say that 80-90% of the results I'm seeing are NOT from the supplements. Looking for a magic bullet? Get the basics down first.
If you're starting out / got a ways to go, I'd suggest just eating fresh raspberries. They're tasty
1) eat real food - more vegetables, moderate meat, moderate fruits, less grains, less sugar, less vegetable oils.
2) exercise - moderate intensity cardio, sprinting, heavy lifting, dedicated stretching and mobility.
3) live - relax, de-stress, meditate.
Disclaimer: I'm not professionally qualified to make any formal recommendations. I've just done my homework and I'm my own guinea pig. All of my data, unless otherwise cited, comes from a sample size of n=1 (me).