how quiet? you've ran Darts, comparable?

To me lifespan is a consideration, but not the only one when making a purchase. Any kind of high voltage (115-120 VAC) device in the salt water makes me nervous, so that was certainly a factor when I decided to drop big money on a spanking new 1st Gen MP40 in 2008. It had it's issues & I've done some upgrades to it over the years, but it is still going strong (& relatively quiet) in my 77 gallon Hagen. This is largely due to the modularity of design. Separate wet/dry side, new drivers compatible with original dynamic components, user replaceable wet side bearings, shaft, propeller.

Despite the poor design of the Gen 1 wet side magnets.
https://tsl4pa.blu.livefilestore.com...net.JPG?psid=1

EcoTech quickly realized the error of their ways & came up with a new design. I was a bit unfortunate that I had purchased mine just before the design change. Nevertheless, I was able to easily replace the magnet with the new one for about $10 at the time. Newer wet side magnet with bearings/washers that I've replace for minimal cost over the years.
https://tsl4pa.bl3302.livefilestore....63a.JPG?psid=1

2009 & 2010 I purchased used MP40s to beef up the flow in the tank. Actually scored a couple more but sold them later, to help pay for new drivers on the ones I am running. No problem finding buyers for the old drivers either.
https://tsl4pa.bl3301.livefilestore....30e.JPG?psid=1

Currently I have 3 MP40WES ranging from 7 to 5 years old, providing plenty of flow in the the tired old Hagen. They actually seem to work better & quieter the older they get. I don't mess with them too much. Toothbrush to scrub loose algae off every month or two. Run in Tidal Swell Mode most of the time, switch to pulse for a while before every water change. If I want a gyre effect in the tank, they are capable of doing that as well.

Might be about time to consider a vinegar bath to restore original flow. Right side.
https://tsl4pa.dm2302.livefilestore....38e.jpg?psid=1

Center back, running as a slave but limited to lower speed due to narrow tank.
https://tsl4pa.dm2302.livefilestore....40e.jpg?psid=1

Left side, this is the oldest one that I purchased new in 2008.
https://tsl4pa.dm2302.livefilestore....41e.jpg?psid=1

I realize not everyone has had the same luck with these as I have, but I can only go by personal experience & they've been a great purchase for me, I'd do it again. I won't be going for the latest quiet drive upgrade just yet, mine really aren't disturbingly loud. I have this running my old skimmer, it drowns out most other sounds around the tank.
https://tsl4pa.dm2302.livefilestore....42e.jpg?psid=1

And I also have an old Hagen powerhead pushing water through the skimmer plus some larger ones I use for mixing up fresh salt water. They've been quite bulletproof and still going strong after many years.
https://tsl4pa.blu.livefilestore.com...17a.JPG?psid=1

No experience with Jebao at this time & not needed based on the gear I have now. I do run cheap generic 10 watt LEDs for lighting.....

No comparison to the Dart. If I put my ear to the tank at the same end I can barely hear them.

that quiet, pretty good.

thinking the rw20 just as being able to dial back, compared to running smaller full on. maybe something smaller than the rw20, tank is only 145g

I honestly think you may not be able to dial 20s low enough. Im running the rw 20s on my tank on the lowest speed setting on a slow alternating pulse. Any higher and the sand at the edge of the tanks first 4-6 inches is non existent. I know its probably hard to believe but you really have to see first hand how much water these things move. I'm confident that two of the 15's would be more then ample. I tried the 15's and would have kept them but the magnets just wouldnt hold for me. For whatever reason the magents seemed to hold better on the 20s even though theyre rated for the same thickness.The overflow end of my tank is 15mm with 1/4" black acrylic. With my rw20s I've doubled up the magnets on the outside just as a bit of added grab. I

Update for the rw 20s. About two weeks ago had a controller crap itself. Fortunately the rw20's were so cheap I bought 4! Two for backup. Dave at Concept if fixing me up on warranty, and I still have another back up :)

Cost is only part of it for me. What it does and how loud it does it matters too. I'm also fussy about how anything in my tank looks. I've had amazing luck with my tunze 6105 which are still going strong in my old 404. Still silent too. My mp10 are still running perfectly too with minimal maintenance.

I've got a Hagen 402 still doing grunt work for me as well but it's not pretty. Hence behind the scenes grunt work I guess lol.