Luckily when I started out the plugins-for-trello space was very uncluttered. It was mostly abandonware and github projects created by developers over a weekend. So since Corrello is exclusively aimed at Trello teams and was one of the only tools being built fulltime just for that I have been able to piggy back on their success without a lot of serious competition. There is some competition and I expect more will come as others realise the Trello platform is a viable place to build a business but I think that can only be a good thing really.