There’s no problem with Meter gauge. They’re still rail companies churning out meter gauge trains.The problem with MGR is availability of rolling stock. Meter gauge is becoming obsolete save for a few countries in Europe. Kenya shouldn't build any new meter gauge rail. Even the existing light rail ones should slowly be overhauled to standard gauge. It will make it easier to procure rolling stock.
It doesn’t make sense spending money to build a 5km SGR track. It’s not smart and literally locks out the rest of the commuter rail network.
We should go for a hybrid system like Japan. Where it’s high speed Shinkasen trains run on broad gauge which is used for longer high speed traveling. And a wide majority of its commuter rail system is completely narrow gauge and fully electric which is used for city commuters and direct airport link.
This is the Narita Express it connects Tokyo City Center with Narita Airport and it moves at speeds of a 130kms per hour.
With system similar like that in Nairobi. A direct link with Nairobi City and JKIA will only take 7-10mins.