I have a late 2009 27 inch iMac. It's now slow for my needs so I decided I would use my 2012 RMBP with an external monitor. I know I can use the iMac as an external display using target display mode but my question is, is this a good everyday solution? I have read posts from people that say doing this on a permanent basis is not ideal. Would getting an external display be better? Are there any downsides to using the iMac as an external display over getting a good external monitor?