There is a really critical known issue with this app, which is that when users convert prices based on the location or currency they want, they are shown a different price at checkout based on the default currency of the Shopify store. There is no workaround for this. We have customers complaining that what they see in terms of the exchange rate is not what is shown at checkout. We would have thought this was a basic feature to get right or to allow the store to manually change the currency rate to match what is charged at checkout.
This is Lea here, Support Manager at Booster Apps! First foremost, thank you for your feedback, and I'm so sorry for your experience so far. I can understand how important it is to convert the prices at the checkout page, that's an ideal setup.
The app itself is able to convert currencies on the product page, cart page, and all across the site, but I'm afraid the reason why we can't change the currency on the checkout page because Shopify does not give us access. This has been planned as an improvement for our app and we are eager to implement this - once Shopify has granted us access to change currencies to the checkout. I'm sorry about your experience so far, and I definitely want to make it right.
Though our app is free, it is by no means at all an app that we neglect and we take concerns and feedback such as the one you're experiencing very seriously and would love to get to the bottom of this.
I've sent you an email as well, feel free to reply back and we'll be happy to give you some more technical information about the app itself.