The stock smoke units can be made to work and rather nicely at that with just a modicum of effort. I think the basic mechanism (the heating element) is ok but it needs to be fed a constant supply of oil to keep it going. The piston pump is too noisy and can be replaced with the ubiquitous CPU fan still utilizing the unit's housing/reservoir.

There's much mention of improving the smoke generator on this forum over the years... check it out.

http://www.rcuniverse.com/forum/m_4681563/tm.htm
http://www.rcuniverse.com/forum/m_5911084/tm.htm
http://www.rcuniverse.com/forum/m_5800130/tm.htm
http://www.rcuniverse.com/forum/m_4562562/tm.htm