Safety -- it's fine, well constructed I would say. Painted metal enclosure is rather nice. The exposed transistor (regulator?) isn't a touch hazard, strictly speaking (SELV is below 70V DC), though you wouldn't want to accidentally drop metal parts on it -- I'd be happy with a metal mesh covering it. If it's just the TO-3 "hot", you may even find a plastic cap to snap in place.
I would check if the enclosure is tied with circuit ground: earthing it is an option, of course you need a three-wire cord to do that, and could perhaps install an IEC receptacle if you're feeling up to a little metal cutting. The reason to check is really just so you know how it's wired. If tied, you can't float it anywhere with respect to other earthed equipment (e.g. oscilloscope ground). If circuitry is adequate isolation distance and everything, lifting it from chassis ground is acceptable, in which case you get the protection of an earthed metal enclosure plus a floating output you can wire to anything.
And if internal ground is lifted from chassis, then you can install a 3rd binding post (green) and shorting bar, so you can earth through the power supply directly, when desired.
The capacitor may need reforming; I guess since you've applied power, that cat's out of the bag. If the capacitor got warm while you were testing, maybe consider taking it up slowly on a variac (or series lightbulb). It might also be dry, but for capacitors of that type, I'd say it's hit or miss; many survive for a long time. In any case, replacement is easy; comparable values are cheap, and much more compact.
I'm guessing the circuit is very basic. A typical project is an LM317 -- it would be the -K version in TO-3 here -- with a transformer, rectifier, filter cap, and pot to vary output voltage. The meters are convenient, and the range switch means more current capacity at low voltages before the regulator overheats (LM317 is internally thermally protected so it's okay to overload, just don't do it for a long time, it can eventually fail).
Compared to other options -- well, it's one supply you don't have to buy, if that's value to you then there you have it. It's only a single output, it's analog movement (though you could patch in digital meters if you prefer), so it's not wildly functional or versatile or accurate. It should be pretty stable, and it will be low noise as long as the regulator is doing its job -- in particular, you don't have the plague of switching noise from those cheap Chinese modules flooding the market these days. It's probably unidirectional, i.e. it can only source current, not sink it; it's not a power amplifier, downprogrammer or SMU. Mind, this only matters when connecting multiple supplies together, or doing things like regenerative braking where current can flow back into the supply.
Tim