Just get d indoor water treatment sys ll do,if you ar budget tight. Coz indoor drinking water much more important than outdoor

Outdoor unit sure need to back flsuh, if you don't install that, your indoor unit how expensive also useless.
Indoor unit you can use carbon filter(rm150 Panasonic), but suggest to use better type filter as this carbon filter won't really remove all the "dirt". Your water supply matters on filter selections.

Outdoor either go for user-replaceable like 3M or backwash flush sand filter like Pentair/any identical.
Any type of filter always come with Pros and Cons. So don't expect a perfect unbeatable system.

Im not a sifus.. i used that kind of set up. Just a normal filter at the main and an activated carbon filter at the undersink. Catridge at the main i change it once in two months, which cost me only rm15 for 1micron filter. Used to used 5micron which cost me rm7 n change it every 4 months. Activated carbon i yet to change it. One catridge cost me around rm15. So far so good. No rust detected at the cattle or any of the piping fittings.

The outdoor unit won't be that expensive, about rm500-800 also you can get, provided you know the place. In shopping centers sure are more expensive, as they charge 2-5X extra.
As for back flush, you only need to back flush it for 5-10 minutes, so use it for gardening or car washing.
The cartridge for indoor unit I only change once a year, rm40, so in some sense, I save more than you.

Whoever asked me, I will recommend outdoor for 3M AP902 and indoor for Amway eSpring, if budget running tight, go for 3M DWS1000. Both having the certified of NSF 42 and 53, while eSpring have bonus UV tech NSF 55.

There are always pros and cons between you choose either membrane filter, sand filter. While 3M AP902 is something like in between both. User replaceable cartridge when reach 378,541liters. While Amway eSpring will be same as well when reach 5,000liters. I can't said is expensive or cheap but is affordable in the long run.

Sand filters got many brand or types, some need to do backwash like every weeks or months for what I have encounter/feedback from friends or families. Don't forget, both sand filter need to change after couple of years and membrane filter need to change as well.

RO water sure taste good because I have one Coway Petit in my office, but in long term usage like at home, I would recommend others instead of picking RO system. While like you said, you don't like the taste of eSpring, it might be possible to early new cartidge just replace into the eSpring, the water came out something strange if you drink for the first time, but after you filter like more than 500-1,000liters later, you won't taste that anymore. I using it too, that is why I know what you talking about.

I have no idea about GE Water brands. Maybe you could share your thought about it, which model and what its feature or what it capable of doing it?

Anyone use 3M AP Easy Complete water filter? is it good?

Talking abt espring i actually feel it fresh. But for taste is quite subjective. U can let a kids try. Usually they can recognize which water is nice to drink. As i get many feedback abt espring taste sweet...kids like to drink water.
I m d one same as you particular wif water. Plus i m a chemist tat y i choose espring. Regarding of one of the model of panasonic is made by alkaline water. Tat y i would not consider it in my list