I haven't tried the penguin sprayer from Spraymaster, but I have had a Mytee BOSS cordless sprayer for about 5 months now, and I love it.
Here's a list of what I like about it:
1) It holds 6 gallons if you need that extra bit of juice, but don't tip it very far if it is overfilled.
2) It is cordless (obvious one)
3) It will easily last you all day on one charge.
4a) The battery level indicator tells you when it needs charged.
4b) You can easily finish hosing down a carpet if it indicates you need to plug it in soon.
5) The wheels make it easy to get up and down stairs when it is full.
6) The tank is removable. This allows for the use of multiple presprays in seperate tanks.
7) It is a heck of a lot faster than using a pump-up sprayer, and more consistant.
8) The fill hose is very convenient, just hook it over the aerator on a kitchen or bathroom faucet.
9) It looks a lot more professional than a pump-up sprayer.
10) It is not so heavy as to make it difficult to lift into the van, even when it is full to the 5 gallon mark.
11) The tank has gallon level marks on it for ease of figuring out how much to add to fill it up.
12) The basket on the handle will hold 1 lb sample jars or even quart bottles. Keep your citrus gel with the sprayer for easy spot treatment.
13a) The hose is long enough to park the sprayer at the bottom of a staircase and still reach the top on almost all straight staircases.
13b) You can also park the sprayer, and spray a whole room from the doorway on small bedrooms. Large rooms only require moving the sprayer 2 times at most.
The only thing I don't care for about the sprayer can easily be solved by not taking it up stairs when it has more than 2 gallons in it. Just put in your concentrate, and fill it with water when you are upstairs.
I 100% recommend that you get the Mytee BOSS sprayer. The time savings alone will allow the sprayer to pay for itself in extra jobs you can do.
Oh yeah, and what Jim said above.