Nothing wrong with a good zoom , just a smaller FOV compared to say a good Plossl eyepiece of the same size , eg a 25mm Plossl will give about 52 degrees where as a zoom at 25mm gives about 45 degrees , its no big deal in an f9 refractor like yours .
But you have a reasonably good low power eyepiece in the 28mm so thats sorted , yes a zoom will suit your scope well .
I am sure tho at the smaller sizes ( higher powers ) like say 8 - 10mm the FOV is similar in the zoom to a Plossl .
Brian.