A newer revision of the dual tuner model is out, Tablo DUAL (2 models actually, one with built in storage and another without) but there are lots of people still running the original 2-tuner model. The actual functionality is basically exactly the same.
It's a glorified VCR (you have to manually schedule the channel and time) if you don't have the service. Still useful if that meets your needs.
I don't think anyone has had any major problems with refurbs.
For $90 you are getting a solid tuner with pretty mature software. I actually moved from TiVo to Tablo because it provides a lot more flexibility without having to invest in additional hardware I don't already have (I already have Roku, Android TV, Android devices) and the service subscription is at the account level, not the device level.