Vitalis Holiday Grazer Review

Hi all! I've just returned from a seven day holiday, and I'm glad to say all of my fish are non the wiser. I currently have:
8 Cory loxozonus
6 praecox rainbows
4 otocinclus - I grew algae for these separately
5 lemon tetra
In a 125l tank.
Before I left I did a 50% water change over two days (which put nitrates around 5ppm), and I put in a vitalis 7 day holiday grazer block. This is like a sucker on the glass which you attach a ring of food to. The ring cracked when I put it on but it didn't break up.
I put this in around 48 hours before I left so I could see if it would dissolve or muck up my water - which it didn't at all.
I've just returned, everyone's alive, and the water is perfect. Ammo nitrite 0 and Nitrates reading 10ppm.
Thanks for reading my review.