Yea, if they go without eating too long during transport then their gut bacteria dies off and they can't process food even they later start eating. I'm paranoid too about mine not getting enough- it's hard to tell with these guys. I just keep an eye on their bellies. As long as they don't look concave and they're pooping a lot, they're ok. I think it took mine a good two weeks after I got them to finally start getting nice and plump.
My floating hornwort is good at staying put. In fact, I use it to corral my frogbit, which does drive me to distraction with its tendency to zoom under the filter outtake. The suction cups are a good idea.
If you got the Super Green, make sure you prepare it right. The first time I did it, I microwaved it too long and it didn't set properly. So, when I put it in my tank it was really loose. Along came my betta, who decided to plow right through it, kicking it up everywhere with his fins. What a mess! That gave me nitrites at .25. Little stinker... Microwave the water first, then add the powder. You can pour it in a small container, put a piece of yarn it and let it set. Instant grazing block that you can hang.