from what I've heard (never actually ridden one) they are decent for trail riding but no jumps. I checked them out at the shop when my sister was considering buying one, here's what I thought.
They are heavy bikes for their size, stock exhaust looked extremely restrictive, stock suspension is soft, the E-start feature is nice but lacks the backup kick if the battery dies, the low seat height makes the bike appealing to shorter riders.
Also, on the how fast it goes question, you'll more than likely never get the bike wound completely out on a trail so it's kind of a moot point, it'll be plenty fast.
welcome to DRN also, you'll find there is a lot of good information here :)