'mini'  and  low birth weight  really  aren't tied together.

There are 'normal' sized  Hereford  with low birth weights,   and  'mini' (which that 1500#  bull  doesn't exactly fit here,  he's just a small frame size)  with  higher than average  birth weights.  
Small frame size  will knock the snot out of  yearling weights. 
a true 'mini'   has a hip height of  45 inches or less.   
that  1500#  may or may not be a genetically  smaller  animal,  he could've been stunted  during his  development,  and  this is how he  ended up.  With 'new, current' bulls   available each year,  it's not worth the chance.  
likewise,   feedlot developed bulls   can  also 'hide' a tremendous  amount  genetic deficiencies too....  There's  no arguing that point.

about the  only  thing here would be  the 1500#  could  mount the heifer  without  crushing her to the ground,  unlike a  2000# one. 
who knows, he may not even pass  a semen  test.

assuming your  cow herd is basically all red,  going with a 'true'  Hereford bull (white mane, belly, and socks)  will get you mostly  red neck calves..  with a  smear of  white here and there.  

around here,  true  rednecks  aren't  discounted one iota for  their  hair color.  

Seeing how you keep your heifers,   use the bull that gives you the type of COW  you want to end up with.    
My cow herd is  about 40%  all black,   30% bwf,   30%  redneck/straight Hereford.   I run  Straight Hereford and Angus  bulls,   my bull pool is about  30 head deep,   and  either  buy or lease  about  10 a year to keep  the pool fresh.  When it's heifer choosing time,  color means nothing.   (unless the neighbor's char  came visiting)