Double ended are fine to use, but make absolutely certain that your fixture has a proper UV-blocking shield over it at all times during operation. The double ended bulbs generally do not have an internal UV shield, and the amount of UV they put out is literally enough to permanently blind you if you're exposed to it unfiltered for several hours in a row. Even shorter exposures can cause eye problems (not to mention all of the other damage it can cause to you and your plants).

The single-ended MHs usually have a UV shield built in (although additional filtering isn't a bad thing). It's fine if there's still some UV release; like many things in this world, a small amount of it can be medicine while a large amount can be poison. Your body needs some to produce vitamin D, but too much can cause skin cancer and eye damage (that's the reason human skin colors tend to vary with latitude -- to ensure that we get enough vitamin D but not skin cancer; melanin is a natural sunblock). As far as I've been able to research, it is unknown whether UV has any particular uses for plants (if anyone has come across papers on this topic, please let me know!), but at the very least, they do have known mechanisms to try to defend against/repair its damage.

In short, a little is fine, but a lot is bad.

Well this is a Philips product and the datasheet of this bulb says: All types are UV-Block for reduced health and fading risks.
So the UV release should be quite minimum or is the glass still necessary?

Here is a link that might be useful: Datasheet

Well, I don't know exactly what Philips bulb you're using, but just as a random example:

MasterColor Metal Halide 150 Watt Double-Ended T-7 4K Lamp with UV FadeBlock

Warnings, Cautions and Operating Instructions

"WARNING:These lamps can cause serious skin burn and eye inflammation from short wave ultraviolet radiation if outer envelope of the lamp is broken or punctured. Do not use where people will remain for more than a few minutes unless
adequate shielding or other safety precautions are used. Certain lamps that will automatically extinguish when the outer envelope is broken or punctured are commercially available." This lamp complies with FDA radiation performance standard 21 CFR subchapter J. (USA:21CFR 1040.30 Canada:SOR/DORS/80-381

Even if there was no risk, having glass over it as a precaution against splashing isn't a bad idea, either.

When something can leave you blind, it's good to take appropriate precautions, IMHO.