I might or might not agree if they make money - but on its face
they increase supply (of cash in our hands) in slow - sluggish - recessionary times (to induce low interest rates and increase inflation which then is super low) - buy bonds
they decrease supply (of cash in our hands) in fast - hot - inflationary times (to induce higher interest rates to slow the economy and attack inflation --- see Volker period) Sell bonds (for those new to this - they issue PAPER that is not money and thus pull out real money)
This period is sort of in between The economy is good but not hot - but the FED has been buying for years to keep the economy from getting deflationary etc.
So - as far as I can read - no one really knows the impact of the huge (albeit slow and careful) DRAW of cash as they sell "paper" and suck in cash