All 100mm slot-in filter system are listed here. Top seller product that boasts one of the least color cast filter that can fit into Lee filter holder.
Haida 100mm filter solution allows a screw on Adaptor according to lens thread, and on the front is a innovatively designed thread to mount a specially designed circular polarizer (CPL). The CPL will not obstruct the innermost slot filter on the holder.
When using with Haida filters (ND1.8, ND3.0, ND3.6) from PhotosphereSG, we had arrange for foam gaskets to be attached from factory and when used with Haida holder, it will be free of light leak problems, which can be a common problem for long exposure photography during the day.
Feel free to check out the reviews done here by ClubSNAP Singapore's largest photographic forum member "Scintillation" and images thread
Photosphere SG conducts regular demos as well to show the how to use the filters, feel free to like our facebook page to get updated events