Maxon invented the Tubescreamer, so they know how to get it right. This is the M branded version of the Ibanez Super Tube Screamer, so it's got 18v capabilities, a 'mid enhance'  control to change where the hump in and a switchable low-end booster. Perfect, really... everything a reasonable player might ask for. 

Model: Maxon ST9Pro+ Super Tube
Made in: Japan, recent model (serial sticker missing)
Type: low-mid gain boost/overdrive
Power: standard 9v supply or battery (not included)
Equivalent new street price (approx): $389aud
Mods: none
Accessories: no box or manual
Condition notes: used, few minor marks, fully functional. Overall: very good condition