Used the Aussie sourced molds and they worked perfectly. Unfortunately things are more expensive here than in the States so you may pay more than you expected for them.
I have only done isomalt gems a few times. i had problems to start with with them sticking to plastic molds and bubbles. I found that once you have made the isomalt you should put it in the oven at 270F for 15 minutes to get rid of any bubbles in it. silicone molds work great, if using the plastic ones put a little crisco/trex in the mold first to stop them sticking. I use a small silicon measuring cup to pour it into the moods which works great. if they go cloudy i give them a little blast with a creme brûlée torch which works really well especially on clear isomalt and i also use the torch to melt the back of the gem a little to stick it to the icing. Dont for get to laquer or glaze them once dried the first time i made them i forgot to and when i went back to them they were a sticky bubbly mess. I have only used isomalt a few times but have researched a lot and these methods seem to work well for me hope it helps