Hi,
there are advantages in closing the loop but way less than the manufacturers claim.
They say the closed loop steppers are faster, more powerful and never lose steps......all rubbish. A closed loop stepper has the same torque/speed characteristics
that an open loop stepper (with the same motor).
A closed loop stepper can interpolate between full steps and therefore achieve greater resolution than an open loop stepper. Also a closed loop stepper
will produce a 'following error fault' should it lose too many steps unlike an open loop stepper which will attempt to carry on despite it now being inaccurate.
These advantages are bought with a considerable price increase and increase in complexity.
Good quality AC servos are coming down in price.....to whit....a Delta 400W B2 series (160,000 count per rev) servo, drive and cables delivered in the US for $380.
A Delta servo (of adequate power) will 'eat' any stepper ever made.
Delta and DMM are two good quality brands that won't break the bank. There are cheaper Chinese made drives but of less certain quality, support and documentation.
Craig