First pick the approval route. The portable 2 kg and 4.5 kg models are BIS approved to IS 15683, and the 6.5 kg and 22.5 kg models are certified to IS 16018 with BIS marking, which is what most Indian Fire NOC work asks for. The EN approved range in 2 kg, 5 kg and 20 kg is built to EN3 and carries marks such as LPCB, BSI Kitemark, PED and MED (the exact marks vary by model), useful where a project follows British or European specifications or needs marine approval.
Then size the unit to the risk. Panels, racks and small rooms are usually covered with the 2 kg to 5 kg portables, while DG rooms, fuel stores and transformer areas need more agent, which is where the 6.5 kg, 20 kg and 22.5 kg units come in, with wheeled versions for the larger sizes. A rating such as 34B or 55B describes the flammable liquid test fire the unit put out: the higher the number, the larger the fire.
Finally check the handling features. Every range uses a squeeze grip or handle operated valve so the user can control the discharge, and a frost free horn that protects the hand from freeze burn. A used and ready indicator shows whether the unit has been discharged, on the portable BIS range and on selected models of the others. Ceasefire gives a 10 year warranty on the BIS range and 5 years on the EN approved range, and FPS supplies, installs, refills and services all of them in Bhopal and across Madhya Pradesh.