Specifically 3D Scribbler

1. 3D Scribbler has great customer service.  They are very generous with their nozzles while you're still in your warranty period of about 3 months from purchase.  Use their website to learn to disassemble the pen.  There is a webpage under "Troubleshooting" and there is a fan-made video showing the same thing.
2. Make everything you can during the warranty period.  While you're still supported, while you can still get nozzles.  Because by the end of 3 months
1. you've either done everything you want to do or
2. you've used up all the filament you've initially bought and you don't want to buy any more (though anyone who is a real artist sees value in buying more art materials)
3. you're tired of the perceived unreliability of having to take it apart every time you use it. 
• I don't see it as unreliable, I see it as part of the medium.  Comes with the territory.  For example, air brush nozzles clog all the time--you have to know how to maintain and fix your own equipment.  Tattoo artists have to know how to rebuild their equipment.  You have to maintain your art tools.
3. Their twitter isn't too active, updates maybe once a week.
4. There is an inherent weakness in the nozzle area of the pen. 
1. With all the dis-assembly and re-assembly, the nozzle area gets pretty chewed up.
2. Be careful with the two really thin wires attached to the pins in the middle of the connector.  They go to the thermistor which is glued to the side of the heater.  When either wire breaks (under the insulator) the pen doesn't get a temperature reading and stops working, you get ERR 01 on the LCD display.
3. Where the nozzle connects to the pen body is essentially a thermal break (aka heat break).  The filament is cold on the PCB side of that wall, and it's hot on the nozzle side.  Filament passes from the long Teflon tube to a short tube through a hole in the heat break.  Signals pass through the connector embedded in the heat break to the PCB.  Where the short tube joints to the heated nozzle is where plastic tends to leak.  If you don't watch it, you will end up with a nozzle full of plastic.  The plastic will eventually push the nozzle away from the heat break until one of the thermocouple wires break.
4. So, if you want to continue using the pen, buy more nozzles.  They're $12-13 on Amazon.  But they're $5 each at the Scribbler 3D website.