I used Bactinettes a couple of times when upgrading from a smaller to a larger tank and moving all of the fish, water filters etc. just to try and help the bacteria beds a little. I also used them on one occasion when a long power cut knocked off the filtration and I was concerned about losing bacteria. They seemed to help a bit but I certainly would not use them in the way some of the advterising blurb suggests for stocking a new tank immediately rather than going through the cycling and maturation process. They cost £5 a shot and - if I recall correctly - I added 3 lots when moving to a 240 litre tank from one about half the size. They are messy to get into the filter as they are like small, squidgy jelly balls and you have to get them into the system in something like 40 mins. (can't recall the time precisely, so if that is wrong my apologies). You also have to get a huge volume of the things into the filter, which can be a problem. If you do use them I found the easiest method was to open the pack and pour them into a sieve as you have to discard the liquid medium that they come in.
I personally found them better than the bottled bacteria products (none of which I have found that helpful) but, as stated, I would never trust any of these things for trying to set up an 'instant' tank, just something to help a little in times of disruption or change.