Just retread my post, poorly written sorry, no the MB is no good for open vent systems as the head is not enough to clean the mag, not that they collect much anyhow!
Eliminator will sort this as you can flush or strip out to clean for both sealed & OV systems, another thing about the eliminator is the magnet slides downwards not up as others, so you can tuck it on the return right under the boiler looks neater! Try that with a MC or TF1!
Another design problem with MB3 is customers cleaning it, without turning off the boiler or pump, or when the pump is on the overrun, I saw this 1st hand, customer slide off external magnet, pump on overrun blows crap straight back into the boiler and system!
On a filter front I am very interested in non magnetic debris capture, we have a small estate nearby with 10 year old open vent systems on 10mm non barrier pipe, which are not on manifolds but 15 mm-10 mm reducers which just block up for fun! The pipes are all behind the plaster board walls on drops, we have now done 3 houses on this estate, after numerous others have failed with power flushes which just make it worse, one lady had 2 rads off, then ended up with 6 off! The debris are fish scale in shape and are non magnetic, looks like lime scale extremely hard, we do a manual rad off flush, after first cleaning out the header tank with a wet and dry vac, or all that rubbish ends up part of the problem.
i would certainly like to see how your filter copes with this scenario