The 'make' of the Firewire case itself matters not a whole lot. If you know it's using the Oxford chipset (900 or 911) then it's golden. I'd find out what brand of Hard drive is inside it. Personally I like #1-IBM #2-Maxtor #3-Western Digital and #4-Seagate/Quantum. Had great experiences with all these brands, just find the IBMs to be a shade faster and much quieter.
5400RPM for DV is borderline. It can work... kinda-sorta. If you really want to be sure you don't drop frames and have skips and jumps in your AV, I'd go with 7200RPM.
You can get an external FW 40 gig 7200 for $200, so that price for 5400 really isn't all that hot.
This company offers a 40gig IBM 7200 external Firewire for $199. No info on the style of the case though... my guess probably just the standard square box. Note: a
60gig is only $239 from these people.
I had a friend buy an external FW HD from Madlogix.
Here they sell an external 40G IBM 7200RPM for $219 and an image of the product.
http://www.fwdepot.com/ is good to just buy the enclosure by itself, and then find the best possible deal you can on the hard drive of your choice and put it in the case yourself.