I have under-the-counter Kent Elite but not using it at this moment as:
- my water supply has TDS in the lower range
- i’ve gone for whole-house water filtration/treatment
- i needed something that can run without electricity for more than a day
- sometimes i get extremely muddy water which chokes puny RO filters in a minute
Right now I am using gravity-fed Pureit Classic UF. Cartridges/filters are replaced directly by the company. But I take care of its maintenance as the storage based units need extra cleanliness. Never used company’s services.
My experience has been pretty bad with the company certified technicians. They’ve already caused too much damage. I’ve used services directly from the companies like Kent, Kaff, Jaquar, Cata, Godrej, Luminous etc. I am now 100% sure that I get such poor service because I live in GawaarGaon, popularly known as Millennium City. 
But I’ve noticed that it saves a lot of time if you fix small issues yourself. From the time you book the service request, it takes 1~3 days to get the stuff working again. If you can replace an incandescent light bulb then I am sure you can replace the cartridges on Kent Grand+ as well. And I am not oversimplifying it… it’s written on the product page that the cartridges are snap fit . Don’t know about Aquaguard Superb as I can’t see its internals.
If there’s some electronic failure then you definitely need professional help but regular maintenance and cartridge replacements can be carried out on your own - after the warranty period expires.
Both of them have similar filtration/purification systems. Aquaguard can also be used as a freestanding unit. Based on the position of it’s outlet, it probably uses few extra parts that can go wrong. Usual practice is to use a pressurized balloon and an extra filter to catch the odor… but I am not sure in the case of Aquaguard.