I was given a Kindle by my OH at Christmas. The idea is fine and Yes there are free books to be had via, in my case, Amazon of which I have had quite a number. Alot of the free titles are quite obscure, so I sent for a CD containing umpteen thousand free books of which I have used some.
To me, if you are like my OH and read certain authors as soon as their books are available in paperback, the books themselves are cheaper in the supermarkets.
I think alot depends on what you like to read.
You can scroll through Amazon for Kindle's book list and see what is on offer, but if you can get these for a Kobo I wouldn't know-- is there a question and answer part in the web site for the Kobo? If they are compatible it could be worth investigating.