Friend bought one for his 1989 Silverado (K1500).
I do not remember if it flashed or had an LCD display because there were no codes to retrieve.
OUTCOME: The choppy running of the engine featuring raw gas spewing from the tail pipe was all caused by crud (oxidation) which built up in the swag of the battery cable. The small branch out (8 ga. wire) which powered the nascent computer / fuel system wasn't getting proper juice.
Picture shows a switch to chose ABS or Engine . Like that . The car was having ABS issues a short time ago .
I purchased the simple Actron OBDII reader several years ago . Been happy with it .
Thanks , :-)