The Rugged is the only HDD from LaCie I recommend for "in the field editing" as they seem to be very reliable in contrast to LaCie desktop drives which are extremely unreliable in many people's experience and I will advise anyone to steer clear of them.
The Ruggeds are certainly great as transfer drives for shipping footage around - I often send and receive them from the UK to Australia so they really go through a bashing with no issues - I have one sat here with a dent or two and it works perfectly.
However they do (as you say) get pretty hot so you are ok as long as you don't use them for extended periods without cooling or allowing to cool.
I mainly use them for low data-rate work so anything up to DVCproHD (100mbps) is fine but HD ProRes may be a bit of a stretch for them even the 7200rpm versions as they average out on FireWire 800 at around 200mbps (~50 Megabytes per second) and ProRes 422 is ~147mbps and ProRes 422 HQ is ~ 220mbps @ 29.97fps.
Although this is not to say they won't handle it - I have managed to edit a single stream of ProRes HQ video ProRes 422 HQ without major problems - a few dropped frames here and there but if you ignore this for non-critical offline work on the go then its fine. They will certainly handle any of the 35 and 50mbps XDCAM-EX formats.
If you are serious about doing "on the go" editing in HD then look at the 1TB G-RAID mini: [
g-technology.com]
or better still the CalDigit VR mini: [
www.caldigit.com]
For both these options I'd recommend getting an eSATA adaptor if your MacBook Pro has an Express34 card slot.
For instant answers to more than one hundred common FCP questions, check out the LAFCPUG FAQ Wiki here : [www.lafcpug.org]