I agree to both of these replies. There's benefit, but I have never had an issue that could only be solved with one. I'm not sure if the technology has changed much but ORP measurements in and of themselves aren't a great way to measure the ozone that is actually in the tank because ORP is a function of the logarithm of the concentration ratio. I'll give you an example of why ORP matters and why it shouldn't be used. First why it shouldn't be used.
The Nernst equation to balance chloride ions in water (hypochlorous acid) and calculate ORP looks like to this:
HALF REACTION:
HOCl + H+ + 2e-=> Cl- + H2O
E° = 1,490 mV
NERNST EQUATION (25°C)
E = 1,490 - (29.58) log ([Cl-]/ [HOCl] [H+])
So from this, five problems.
1. There is no temperature dependance shown ( Except what I provided outside of the equation itself as an example). ORP measurements are almost never temperature compensated.
2. ORP depends on chloride ions, pH[H+], and hypochlorous acid [HOCl]
3. ORP is a logarithm of the concentration ratio as previously stated.
4. The coefficient prior to the log which holds a value of -29.58 is (59.16/n), where "n" is the number of of electrons in the half reaction, in this case, two. This negative coefficient symbolizes for the logarithm that a 10x change in the concentration of Cl-, HOCl, or H+ will only change the ORP ±29.58 mV
5. Typical accuracy of ORP measurements are ±5mV because they are given as an exponent of 10. This means based on our above formula that the calculation can be as much as ± 30% off in terms of calculating accurate concentration. Drift in the reader or the probe will make this error bigger.
Now for why it's good:
It measures titration curves really well so any oxy redox reaction that goes to completion shows a measurable change in ORP at the equivalence point. The most basic example of this is pH balancing test kits with a color change. When the color changes, the ORP changes with it and this can be measured to prevent going past the equivalence point.
Overall I just recommend not worrying about ozone or UV. Tanks do fine without them. If you were dealing with a public aquarium and had to keep the building smelling clean because your skimmer can stink up a building, or you are taking in coral from all over the place and want to limit what you deal with, then ozone/UV makes more sense. As far as dinoflagellates go, I recommend supplementing with Iron and Silicate solution and having a big enough clean up crew to work on the diatoms afterwards. Lots of people don't have big enough clean up crews for the size of their tank. I have a 40b with 3, maybe even 4 Purple urchins, 3 emerald crabs, a 2 big Mexican turbo snails, 10 blue leg hermits, and probably close to 50+ astrea/trochus/nerite snails.
I still have algae build up but I never have problems like I see in some tanks and my first recommendation is get a bigger clean up crew from somewhere like Reeftopia and quarantine them for 4 weeks before adding them if you are concerned about diseases, or you can use inverted reef which is pre quarantined invertebrates.
I know some people here do hate longspined urchins but I find they are excellent and if you're careful then your odds of getting poked go way down. It usually when you don't know where they are that you get poked.
Just my two cents. It's not worth the hassle and even though I can defend it, the idea of using ORP as the measurement is flawed and it will kill your fish before it kills your, "pests".
Best practice is to quarantine and treat in a separate tank system. It's not high tech, but it works.
For getting rid of smells, just put a bag of activated carbon over the top of your skimmer collection cup.
For getting clear water, use calcium carbonate powder in solution. I can provide the solution later but right now I have to finish making pot roast

it's at the halfway point where I add carrots and such.