Why should they be any different to the VP ones (except cheaper). I would assume they are made of the same stuff? (zinc).
How long they last usually depends on a number of environmental factors - whether your engine is properly isolated from stray currents and whether your neighbours pay proper attention to electrical isolation. One yacht in our marina next to a large power yacht has its anodes eroded every six to nine months, whereas a similar yacht, three pens away, changes them every couple of years.
I now get 2 years out of the larger collar anode and change the three thin anodes (the ones you are talking about), once a year although I could probably get longer. A few years ago, they were eroding much faster until I took to isolating the engine completely ever time I leave the boat. It made quite a difference! (I have a VP D1-20)
Regards
Tony