What hazards are with this pen? It's the one I've been told by basically everyone is the best. It's flux, so the purpose of it is chemical in nature.

Kester also has a no-clean pen which I've also been told about (I'm hanging with some electrical engineers). It's more expensive, but certainly less chemical-y. And Amazon ships it, so you might be able to set up fulfillment by Amazon and avoid other shipping issues (it's a workaround, but it might work). I'm sure that Kester might be willing to work on it with you, as well, since SparkFun does volume.

Just some ideas.

No! I need more flux, I'm sure it is safe... enough.

Not shown on the photos, but the pen has hard porous tip, with very usable push-doser and holder. It's so cool, I like it.

I absolutely love this pen. Too bad I can't buy it from SFE, but I just found it at Allied Electronics: http://www.alliedelec.com/search/productdetail.aspx?SKU=70177953

If you guys buy all of them before I can place my order, may the back-EMF of 1000 motors attack your motor controllers!

So…what was the danger with this? I've been using it for over a year now and am wondering if I'm going to suddenly pass out and die or something the next time I use it.

If you are in the Boulder area and hurting for flux pens, JB Saunders finally has some back in stock.

Glad I bought this while it could still be shipped. And thanks Asuraku for the suggestion of kimwipes. I'm gonna get some right now.

I've tried this flux and it's working well.

But effectively a big warning if you don't clean the flux after using it, because it is more conductive that you might think.

I've used this to transplant a super gameboy cpu to a gameboy and it was not working after the transplant. i've seen like a electrolysis between cpu pins (SMT) when power was applied. anfter cleaning the board everything was working fine ..

When ever I want to try a new surface mount technique I use this kit: http://www.electronickitsbychaneyelectronics.com/DELUXE-SMD-LEARN-TO-SOLDER/productinfo/C6719/

It has practice parts and a red greed led blinker using a 555.

I used the flux pen to solder this kit. I licked it. It stayed wet long enough to do a few parts. It washed off easily. I used the dedicted toothbrush to scrub the board. Then the heat gun to dry and evaporate the water.

I do prefer water based flux. No chemicals required to clean. And it does not become a sticky as the no-clean stuff.

nice little flux pen very easy to use, to clean just use Rubbing Alchol (I use that stuff for everything but in a well ventaled area but if you are using flux you are allready going to be in one so I guess you are okay)

Kester's 2331-ZX data sheet says cleaning is recommended, as below. So are people actually washing their boards with DI water at 140 F ? Just curious.
"...It is not recommended to use high mineral content tap water. Otherwise, tap, deionized or softened water may be used for cleaning. The optimum water temperature is 54-66?C (130-150?F), although lower temperatures may be sufficient."

This stuff is more conductive that you might think. I was working on a high-gain instrumentation amp circuit prototype on a board with no solder mask and the the resistance between adjacent traces was a megaohm or less!
That's many microamps of leakage in the circuit and it drove my circuit to the rails and caused all sorts of oddball behavior. A solder mask would have reduced the interaction area between the traces and the flux, but the it still would have caused problems.
If your circuit will function with megaohm resistors sprinkled all over you may not have to clean before you test, but you should.
Also, the stuff is corrosive and will cause problems over time.

Is the solder flux conductive??

This is the best way to improve your solder joints. This stuff works great, very good flow, easy to clean, and easy to apply. Made more of an improvement in my solder joints than a temperature controlled iron or anything else in my toolkit.

I tried several varieties of Kester flux and this one is by far the best. It stays liquid for a long time in the tube, it's easy to dispense, and it is an excellent wetting agent for liquid solder (especially the finicky lead-free stuff I'm using).
Its only disadvantage is that it does conduct electricity (a little) when dry, so you really should wash your boards afterward. Well, probably not ... except if you're soldering triacs for use on line voltage because otherwise pretty sparks will result.