Most people use some sort of plastic container to acclimate i.e. 5 gal
bucket, plastic tote, ect...
Point of placing the 25W heater on a small piece of base rock is to alleviate fears of the heater melting the plastic. IME my 25W heater has never melted any plastic container for acclimation but most people feel better knowing the heating element isn't placed up against it.
For fish acclimations of up to 2 hours I agree that a heater is typically not needed (depending on the fish) but with Sea Stars needing longer acclimations due to their increased sensitivity to changes in ph/sg
/temp I would highly recommend using a heater.
Or as I said before using a QT to match the Sea Stars water so acclimation can be a quick 15 minute drip before adding.