I think the reasoning is that it presents itself as an unfair advantage to those unaware of the apps and other third party services. I didn't know this app existed and would have been at a disadvantage. I don't plan to use the app either and it would only make sense that the team at SE bans accounts relating to this. The MB is already very competitive and even more-so after the servers being sewn together. It may be an unpopular opinion here but I agree with SE and their mindset of disallowing third party tools / parsers for an advantage that otherwise wouldn't be available in-game. It's unfair for the vast majority of players and is clearly stated in their ToS. A good compromise could be to be able to see market prices across different servers without having to teleport to them or merge all MB in servers in a datacenter together. I'm not saying this is what I'd like to see, just what seems to be viable options for those really wanting something like it.