Like the Retron series by hyperkin and the like?

I ask because I'm interested in the Retron5 even though it's an emulator rather than a hardware clone.

Anyone have any experiance/opinions?

I have original consoles but it would be naive to have something plugged into my big flatscreen as well.

Also does anyone know where to actually buy one?

I bought one a while back that emulates both NES and SNES. I don't know much about other than it was cheap at only 40 bucks. I have heard some of the system emulators for various older consoles have some compatibility issues.

I have a FC-Twin and a Retron 3.  The FC-Twin supports NES and SNES.  The Retron 3 is NES, SNES, and Genesis.

The NES side of these always has some problems.  Basically, Castlevania 3, and some others, never work.  Sound and color are very slightly off, but it will probably not be noticable unless you're really familiar with the games.  But generally compatibility is OK.  You can play most of the common games you might want to play.  However, flash carts probably won't work

The SNES side of these things usually has the same notations as the NES side.  There's a few games that won't work, but it's a smaller list of non-compatible games.  Once again, flash carts don't work.

The Genesis is usually very well supported on these things.  As is typical color and sound might be a tiny bit off, but compatibility is almost 100%.  I've never found a Genesis cart my Retron 3 doesn't play.  But, say it with me, flash carts don't work.

It has been a while since I've had my FC-Twin hooked up, but I think it supports original controllers.  The Retron 3 definitely supports original controllers.  The catch is that SOME controllers don't work.  The best bet is to use first party only.  Don't worry about the default controllers which come with either (they're absolutely worthless).

Their only video/audio out option is composite.  They're passable for a big screen, but better used on a tube TV.  

Amazon has the Retron 3 and the FC Twin.  

eStarland has the FC Twin in stock.  eStarland is passable, and I would find it acceptable to deal with them for an item like this.

The Retron 5 is out and uses emulation to play NES, SNES, Genesis, and GBA cartridges (not rom images).  I can't give you any further information on that one, as I decided to skip it since it was just an Android device running an emulator.

I have a GP2X Canoo, which isn't as much a clone but was built with retro console emulation in mind. Support and production have died along with the parent company, but used machines still show up.

It performs well up to the 16bit Sega Genesis.
SNES/Super Famicom emulation exists, but brings the system to the limit and often breaks, especially if fancy Mode 7 sprite rotation is involved.