Plastic bucket is fine for most occasions..
Only if you're fermenting at cool temps and expect the fermentation to carry on for a few weeks, would you really worry about alcoholic fermentation in a carboy
You would still want to transfer to a carboy when the activity starts to fall off and the SG is getting around 1.020 - 1.010, because sometimes meads will ferment normally for the first 2/3 of the process and take forever for the last part to finish. If thats the case, you'd want to get a good deal of the sediment from the bottom so that there's enough yeast to finish the fermentation. Then when your SG is the same for 3 days, rack off the sediment so it doesnt make off flavors