In terms of "erasability" it's more than acceptable for the cost of it. Basically if you erase something within a few day it erases fine with minimal ghosting. If it's longer than a few days then you need to erase a little harder or use windex, which works just like the dry eraser liquid.
Having used the very expensive whiteboards at my previous job I don't see a big difference. The expensive ones still left ghosting and needed to be cleaned every week or so.
Lastly, I would experiment with markers. I've found that some (brand and color) erase better than others.
For what it cost, I definitely recommend doing this.
EDIT: Here is a picture of my whiteboard. https://app.box.com/s/jby2cznhev66ec1izvck
I really like what you've done with your setup, that black moulding looks really sharp.
We also used Tabasco sauce for tough marker residue.
It's worth experimenting with different brands of markers and different colors to see what ends up easier to clean if left around for any length of time. If you really want something lasting, take a picture.
(I have a laptop-sized whiteboard I use like that: sketch out stuff, if it looks good, snap a picture to save it.)
For $80 it's much more affordable than actual whiteboards while clearly outperforming cheaper alternatives.
The ghosting ends up being a pretty big problem. We found some window cleaner (not windex) that does a pretty good job cleaning it, but the boards are getting more and more worn over time. Eventually I hope to replace them all...
I've ended up going a different route in my home office, and it's been quite successful.
Ikea sells these long and skinny white-colored glass. 63" x 19" for $32.00 USD.
http://www.ikea.com/us/en/catalog/products/80160645/
I have two of these mounted on the wall forming a pretty good-sized white board. It's a little bit weird with the seam in the middle, but it matters less than you'd think. The glass ends up looking WAY better and classier than the shower board would, and you don't have to worry about ghosting ever.
The price for the 8' x 4' whiteboards: $13. Great value. You can have them cut the panels at the store into 2 x 4 foot sections if you don't have a way to transport the full panel.
I also just use an alcohol/water mix rather than real whiteboard cleaner.
I use normal drywall screws with a countersunk washer which helps the looks. https://www.google.com/search?q=countersunk+washers&tbm=isch
I bought three other "real" whiteboards from big box stores or office supply stores (for about 5x the price each) in the 6 months prior, and every single one has had the surface peel and bubble from the backing, so some areas of those whiteboards are now pressure-sensitive. They are unused since mounting the new board and will eventually find their way out of my possession.
We have moved on to http://www.ideapaint.com/products/ideapaint and are really happy with the result. Cheaper then traditional white boards and better then the Showerboards. The room we tested it in currently has had it up for a year and still works well and easily erasing things that have been up for a month.
All of our old traditional whiteboards mysteriously appeared after a few weeks.
One thing I noticed with the one I previously built was that different color / brand markers made a big difference in how easy it was to erase.
IIRC red and black Expo brand were the hardest to erase while green Expo would wipe clean even after a couple months (we left a couple of test marks on the board once we realized color made a difference to see how each fared).
At the office, another business uses a thin magnetic sheet with magnetic whiteboard tiles they can move around, write on, etc. Means that anything likely to be written up for a long time is usually isolated to a small replaceable piece.
The smoother and harder the surface, the easier it is clean. The actual whiteboard material is very smooth and hard, almost like porcelain. Glass is an ideal surface, so long as you don't have children around. Windows work pretty well too.
References:
http://mywhiteboards.blogspot.se/2012/06/melamine-vs-porcela...
http://www.whiteboardsetc.com/laminated_panel.htm
http://dryeraseboard.com/aluminum-trim-porcelain-steel-marke...
http://www.usmarkerboard.com/s/Unframed-Whiteboard-Material/...
http://www.amazon.com/GoWrite-Dry-Erase-Rolls-White/dp/B0037...
I hated them so much that I keep an eye on CL and I wait for the magnetic dry erase boards to come up. They cost so much that the enamel ends up being very high quality. I got a 4x8 one used for about $150 when I needed one vs the $500 or so it would have cost new. It sucks having to wait but having a dry erase board actually ERASE is just so nice.
Besides being hard to erase and leaving ghosts behind, this stuff does NOT cut easily. The finish is very thin and will chip like crazy when you try to cut it.