Generally it is a very good game, but since you published it here you should adjust one thing. As you stated: just use tokens. That leads to a conclusion that sanctuvex is right and you should adjust the prices for the browser version of the game. Some people will come here for the medals and playing the game on Google Play won't make them unlock it.
Speaking of the medals: it would be good if you made the game check the highest wave reached, so the medals would unlock instantly after loading the game after you will make all the medals work.
Oh, and one last thing I just noticed after buying the first upgrade: remove that dumb timer from this version. There was already one game here that made people wait to be able to do several things in the game and it was terribly received because of that. Forcing people to wait 5 minutes just to be able to buy another upgrade of one type is ridiculous.
I see some improvements and that results in a rise of my score, but I still got some concerns over the gameplay. I see you did not reduce the prices of the upgrades which will make the game a bit grindy. I assume that the different ships have different proprieties and the more expensive ships are stronger? Making them different only in the matter of the look (skins) would be a bit pointless.
One major question: why if I still got the continue tokens and I reach the point at which I get a screen that suggests me to watch an ad for 100 gold if I click on continue button I am still being taken to the menu screen and cannot continue?
And a suggestion: is there any indicator showing how many times I can get hit before getting destroyed? I saw that 2 ships icons on the top right side of the screen, but they never change.
A last question: why every time I enter your game my browser asks me whether I allow it to track my localization?
Just one lastest question: why after I entered the game again all of my bought upgrades just vanished?
I just checked it again: every time I buy an upgrade, leave the game and enter it again the upgrade is gone.