Easy Model's "Selbstfahrlafette" is definitely not a bad model - what I do not like are the tracks, which just look like cheap plastic (no wonder, in fact they *are* cheap plastic).
If you want to know more about the real thing, just google for its nickname "Sturer Emil" - some informations in English language can be found under
http://www.achtungpanzer.com/heu.htm#128