Digital BW, The Print

I recently bought a set of MIS refillable cartridges for my Epson 2200, these are the type that have a filter in the front section.  I asked MIS how many times these could be refilled but only got back a vague answer of a few times.  I know when refilling OEM carts foam can forum in the sponge and start causing problems after a while, don't know if these carts will do the same.  

Anyone have experience with these? Is it better to keep them topped up, say refill when the are half empty or ??

Thanks for any advice

Tim