I used the Stealth 50 with cadence/speed/heart rate sensors from last Fall until two months ago.
I really wanted to like the computer and sensor. The hardware was not typical Cateye...top notch and a bargain price. My hardware failed almost immediately after purchase. It did look good on the bike, it is easy to read at speed and screen changes are fast and intuitive. Setting up the Stealth is not all that intuitive and the user manual sucks (to be fair, Garmin's user manual sucks equally badly).
Sadly, the firmware and software sucked. I had great difficulty getting the ride data off the computer and uploaded to the Cateye Atlas website...when it finally worked on the sixth or seventh of twentieth try at getting the data off the computer head and onto the website my cussing subsided to merely hurling invectives at the software team that wrote that crappy code.
Cateye customer service gave me a second, free computer head and also a free heart rate strap when they finally failed. They did so willingly and with a smile, fully aware they had a problem child product on their hands. Great customer service...backing up a poorly designed product that was, perhaps, rushed to market?
Although the second, freebie units were holding up well the glitches in the firmware got to be too much to deal with.
The Cateye Sync software program that uploaded to Cateye Atlas has the very much appreciated feature of uploading ride file data directly to STRAVA and Training Peaks. Garmin's 'Garmin Express' software that is used for device firmware updates and can be used to upload ride file data to Garmin Connect website really needs to add these options. It's a time saver to have and avoids exporting a file in GPX/TCX/FIT formats to then upload to Map My Ride, STRAVA, etc.
Meanwhile, Garmin prices kept dropping and I bought a ended up buying a 510 to replace the frustrating Stealth 50. The Garmin has been reliable, easier to use and has more functions (which you may or may not want/need, but I like them). The 510 is highly configurable to suit individual preferences for displays of data. You can display up to seven data fields per screen with 5+ screens of data available. Overkill or not, you CAN make those screens display exactly what you want to see and in the format/size that pleases you.
The backlight/night screen display on the Garmin 510 is better than the Stealth 50, but I never had difficulty with reading the Stealth in bright daylight or at dusk/dark.
The Garmin 510, despite some internet negative reviews, is light years better than the Stealth in almost every respect IMO. The only feature I can't find on it that I would like to have 'back' (that was on many of my older computers) is the up/down pace arrow. The 510 does incorporate a air temperature sensor and it seems to be pretty accurate.
The only other negative I can say about the 510 is the rubber plug that covers the proprietary cable connector's data port. I can guarantee you it is not waterproof or even very water resistant. Of course, how water tight is any electronic device? I bag mine when I get caught out in heavy weather any ways, so it's not a deal breaker for my use. Oh yeah...screen changes are just a bit slower than I like. No biggee as I usually only switch between my main data screen (speed/distance/elapsed time, heart rate, cadence, etc.) and my altitude/climbing screen.
I bought the 'bundle' deal and it comes with all the sensors stem/handlebar mount and a Garmin branded 'out-in-front' Barfly style mount. Price on the 510 bundle are down to just about $300. Last Fall the Cateye rig with sensors/strap ran around $225. Garmin 500's are priced at fire sale prices, if you shop around and find a dealer trying to close them out.
I'll use the old Stealth on my indoor training bike this winter.
My advice? Either buy a Garmin 500, which is now priced almost the same as the Cateye unit or go with the 510. The 500 is considered a rock-solid unit and offers almost every feature of the 510 except the 'cool kid' touch screen (when did buttons become obsolete and why, then, does the 510 still have three of them???) and Blue Tooth phone sync feature to brag about your ride to your equally connected friends 'in real time' or do things...I'm too old to figure out how to do or 'why' I want to do that anyway!