CM3-4PM1 is slightly weaker. If u r happy with CH2-50PC then get back CM3-5PM1, if u wan something a little weaker than CM3-4PM1, price difference RM 50 only, hence most customers get 3-5

Get grundfos Scala 2 better for your case.

Regarding pipe burst, many forumers asked this question as well. Pipe burst has nothing to do with the pump but is due to the poor installation of the pipes. Why other houses or condo install CM3-5PM1 did not burst or leak while some YES. reason is the pipe not the pump. If old house and you have no confident with the pipe, scala 2 with variable speed is a better option.

best to have a tank but most condo do not have a tank,

Grundfos Scala 2 would b good. However, if your unit is at the 10th floor, pressure should b quite strong unless 10th is the highest floor

Always after filters and placed after tangki if you're in landed dwelling. You want the pump protected. Most important criteria for the filter must be able to cut out mud, silt, rust. If you use those stone and sand media, protect it further with another layer of 10 micron pleated filter before it enters the pump. With membrane or 3M AP902 that won't be necessary as it is already protected at point of entry.