Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Think twice before buying this product (unreliable)

Bought the previous model HD841 whick looks almost identical.Unit 1-Upconverter feature breaks return get new unit.Unit 2-Upconverter feature breaks ship to Samsung to fix. Board replaced.Unit 2-New board, upconverter feature still does not work.Getting ready to screen at Samsung. Generally Pissed off.