Can you actually enjoy the game without having to give them your credit card number?
You don't have to pay to have fun playing MWO.
Some friends to join a server as group is more important than paying money.
The point to spend money is reached then you want to level up more than two Mechs - then you need additional Mechbays.
Except that, real money (Mechwarrior Credits) is more or less a way to speed up the earning of ingame money (C-Bills).
As member of the winning team you will get around 100 000 C-Bills, a light Mech cost up to 3 000 000 C-bills, so after 30 Wins you can buy a new Mech.
Spending real money on Premium Time will increase the amount of C-Bills earned by 50%.
Instead of waiting for 30 wins, you can buy Mechs directly for MCs.
Personally I would spend real money only for Mechbays and to change the colour of my Mech, and only if I'm part of a Merc Unit with specific colours.
I would also spend money to show the Merc Units Crest on my Mech.
MWO is not pay for win, that's a big pro.
On the bad side some things are still annoying:
The tools for Teamwork and communication are terrible. You have to go to Battlegrid (2D Map) to set orders, and almost nobody will follow them.
Simply aiming at a Control Point or a place on the Map and setting an order (like in Battlefield 2 or Bf 2142) isn't possible.
There is a commander mode, but nobody is using it.
There are no points for following commander orders, and to give orders you have to go to Battlegird, becoming a sitting duck.
There is no Ingame Voip to communicate with the other players of your side, and there is no quick chat like in Battlefield or Freespace.
The lack of coordination and communication is a server disadvantage if you play against other players that start in a premade group with 2 or more players.