Cheap moisture meters are perfectly reliable if you learn how to use them right. You have to calibrate the reading to some independent measure of moisture (like your finger inserted a couple of inches into the soil) and then you can rely on the reading to tell you the same thing each time. People who tell you they are unreliable either had a defective unit or failed to learn how to use it.
Cheap light meters are usually very helpful and should be completely adequate for your needs. They will tell you a lot about the different areas where you could grow plants. There's no need to concern yourself with the spectrum if you're just checking natural light (which has pretty much the same spectrum everywhere you might look in your house or patio). There is definitely no need to spend lots of money on a light meter for color correction unless you are measuring artificial light, as they are no more reliable than a functioning inexpensive model. The technology for an informative light meter is pretty basic and does not require rocket science.
I recommend walking around your house and patio with a light meter and putting it in different locations at different times and seeing how they vary. A quick survey like this may change your mind about where you choose to put some plants. What's important is not so much the absolute number but the relative amount of light, which varies on a log scale and may be 100 times brighter in one location compared to another.
I have both types of meter and have gotten a lot of valuable use out of them.
Most cheap meters that purport to tell you fertility are not accurate and should not be relied upon to decide when to use nutrients. Stick to a schedule, and measure the nutrients, and stay on the low side. If the soil is fresh then nutrients are overrated for most plants anyway.
Cheap meters that purport to tell you pH are also not accurate and should not be relied upon. Use a reliable test kit (like the cheap drop test kits sold in your local aquarium store for $5) to test the pH of your water accurately. If you are going to adjust the pH of your water (which is pretty much unnecessary for most plants if your water is near neutral) it's important to be consistent about the results. I actually adjust the pH of our very alkaline well water (pH>9 out of the tap) to near 6.0 for my plants (mostly succulents) every time, and would recommend doing this but only if the tap water is extremely alkaline like ours. Also be aware that the product pH Down contains phosphoric acid and will boost the phosphate in your soil significantly if you use enough of it. I prefer a product called Acid Buffer (Seachem brand) which is bisulfate and does not flood the zone with phosphate.
Any time you adjust the pH or add nutrients, it's important to flush the soil with extra water each time you water, so that the added salts in the water do not accumulate in the soil over time.