One disadvantage is that if you buy it from taleworlds website steam will not give you a refund if you have some problem with the game( for bannerlord there is no chance that i will ask a refund but i am just saying )
Why would people refund an early access game? This is a mainly a singleplayer game, this is not Last Oasis.
After all if people want a refund for an early access game they shouldn't have bought it in the first place.
Also you will be able to get 20% off Mount&Blade II Bannerlord purchase for the first 2 weeks, the price will not change again until it releases, or its very unlikely, so why would people refund? to pay extra when it launches?
TaleWorlds Entertainment -
"There is no plan to change pricing after early access."
Also I don't know what you mean by "if you have some problem with the game, Steam won't refund you", well if the game wasn't bought on Steam its kind obvious they won't refund your game, however, TaleWorlds Entertainment
(support) will help you out if you have a problem with the game
or with the key, they might be able to refund you but not sure because I will buy the game and I don't want a refund so I don't know how it works.