Can you pay it off in full before the 0% ends?
2% is charged on full transfer rate, not your declining balance so your APR may actually be the same or more as SL.
Eg you will pay 2%*$20000 = $400 on an avereage of $10,000 borrowed over the year if you pay it off. This is a 4% rate.
Even minimum payments may be as much as $600 per month with some cards, averaging $400/$16500, or just under 2.5% interest.
Your SL payments will not end so you will add $600 to $1800+ to your monthly payment for at best 0.25% on $20k, or $50 saved.
Not worth it. Pay down SL by that the extra $month instead. Wait for 1% or lower balance transfer.