If the salts are overdosed in the arc tube the lamp will constantly flash as the salts try to settle but aren't able to

there time bombs

They're a hassle to deal with.

WAY too much mercury in them. The fact that they are timebombs means they are the worst polluter in term of mercury polluction.

Positive thing about them is they overpower the HPS

Hard to see under when used as streetlighting

They're the closest thing to "sunshine in a box." Good CRI, the light can be focused into an intense beam, and the light can be made to emit various colors without coloring the glass or adding a phosphor.
Yeah Jace, I know I'm not following your rules 

They allways needs a shield ( Glass) cause of the intense UV radiation and cover up the exploding lamp- even when EOL-(Except MHs with shatter proof)

Well, on the con side, in my experience they never seem to last their rated life. Not that any bulb is guaranteed to. Just seems they arent as durable. In large 24-7-365 installations, it's either impractical or people (myself included ) forget to give them  their required weekly shutdowns. On the pro side, they kick HPS's arse appearance-wise, and will be the only source that looks close to mercury for the foreseeable future....

The ceramic MH arc tube may just crack instead of exploding like the MH with quartz arc tubes.