promacjoe2:
question, What is the voltage/current that you're trying to control. If you're trying to switch 120 VAC or more, Do yourself a favor, Don't use Hobby type relays. Get yourself a good SSD. The kind with the built in screw terminals. Alternatively you could use remote control power outlets if you're trying to control Lamps or other plug-in devices. One that is commercially made, and UL approved or its equivalent.
in my opinion, Most of these Hobby type relays are not suitable to switch anything more than low-voltage/low current. Nothing more than 24 V DC or 50 V AC. For test purposes, when you're monitoring everything constantly, they are fine. But I do not trust them for continuous use. The relay that you show is a good example. The low-voltage side of the relay is in close proximity to the high-voltage side of the relay. This could allow an arc to damage your Arduino, and possibly cause a fire. when doing home automation, safety is a big concern. Things do happen, but you don't want to endanger your life or your family's life/home just to save a couple of dollars.
First off, there are times to use solid state relay, good times, bad times and dangerous times. To simple throw mechanical relays under the bus and say go solid state is just plain bad advise. I don't care if they do have a UL approval(which is really funny you mention that, but I'll come back to that point) there are times that solid state relays can be downright dangerous. The first application that comes to mind is any type of heater application, especially one that generates pressure, like heating water or worse, oil. The core issue is that when an SSR fails, they almost always fail closed with their output(s) on. And they do fail, at a much higher rate than good mechanical devices (within their rated lifecycle times), especial when driving inductive loads. So, you've got to design for that, there is no free lunch. I could go on but its late.
Now, you're shown a picture of UL listed relay and you call it a hobby device. Curious. Just what kind of mechanical relay do you consider non-hobby? We can argue that maybe the core issue here isn't the relay at all, it's the pc board it's mounted on. Granted, I don't see any routing of the board to increase the creepage and clearance distances. But, does that make it unsafe? No, not at all if it is used within the ratings of relay itself, otherwise it would never have been given UL approval - due to the pins being too close together to meet the UL creepage specs. After all, it is a pc board mount relay.
What wasn't addressed in your oratory was in fact the biggest issue, IMO. The fact that the relay is a directly driven 5 volt device is where is where it falls short. Had this been one of the commonly available opto-isolated relays, I'd have no reservations whatsoever with its use. As it is, it does present a hazard to the Arduino or what ever may be driving it, should the output being controlled fail and the installation lack proper fusing to prevent fusing of the copper traces on the load side of the relay, thereby creating a small arc flash event and possibly coupling the HV over to the LV side in the ensuing plasma ball. This hazard exists within any system, hobby or not, generally speaking when potentials are above 50 volts - which is why circuit protection is such a critical issue. Use the correct fuse, both in amperage and time rating and there is no hazard.
Sure, everyone is entitled to their own opinions. But, not their own facts. I would argue that the facts say that ain't no hobby relay. IMO, a hobby relay is one that has no ratings or international agency approvals printed on it.
Although the Songle relays seem to be okay (if there are not also imitation Songle's ::))