Sure, no difference. But I use it properly. For example, to intimate person "-eru", but to persons of higher rank and stranger "-eiru". Japanese is troublesome... A lot of other words that have been simplified exist. "mirareru" is "mireru", "taberareru" is "tabereru" and so on... Though the meaning runs, it is grammatically a mistake.

There is no difference whatsoever. "Wakatteru" is just fast speak.