Pros: low cost, power, reliable, grip, easy servicing, parts & accessories
Cons: prone to dirt, quality control, switch quality, cost for value
For an executive summary, read only the bolded items.
The Dremel 100- N/7 is Dremel's entry level rotary tool. It has the key features that made the Dremel tool famous over 50 years ago. Its functionality is proven by years of predecssor models but no functional changes, decades old models are still in use today. As its very basic, it should work as nearly reliable as older reputable versions given cost cutting, reduced quality control and planned obsolescence plague modern tools.
Why a 100 over the flagship Dremel 4000? If one works on a bench doing precision crafts, electronics, or detailing, the older design Dremel [ Model 275 and earlier] worked very well, without resorting to an accessory like the flex shaft. The 4000 provides more power, but also it has more unproven new parts, internal electronics that serve as points for failure, more bulk, and higher costs. The 4000 is more like a lightweight contractors tool and maybe acceptable if you find the original Dremel underpowered for your type of work. You may need to buy a grip or flex shaft accessory when using the 4000 for detail work, because the added size provides less precise grip compared to the smaller, lither 100.
Dremels rotary tools are only high speed motors with right mounts to take attachments, so little can go wrong. There is no gearing. It uses proven reliable brushed motors, but need periodic brush maintenance. Over time, use, or contaminated with dirt, motor innards will wears, even with the best of care. Thus, its important over time that a Dremel have economically priced replacement parts because the quality of future consumer power tools has worsened with time, so maintaining a known good model is more important that discarding it. Unlike other rotary tools, Dremels are widely made, so most parts are cheap, plentiful, should they be needed.
Simple design: although some old Dremels may have discontinued parts, the simplest models often can use many modern parts interchangeably. For example, the Dremel 100 is just the Dremel 275 with updated parts, which is similar to the Dremel 270 of ~ 30 years ago.
It provides the highest speed as found in the top line Dremel 4000, so the 100 has the basic functionality of the series
It uses most all accessories
It has a smaller ergonomic shape for grasping, found in the older model Dremels
Spare parts are easy to obtain from Dremel or its distributors
Its easy to fully disassemble
Its armature does not use the plastic flex coupler found in prior models [ its prone to wear, and eventually break, causing the motor to spin, but not the shaft. While only $2-4 each, you'd have to order and replace it yourself, although some users have found thick plastic tubing can substitute for it until you get a hold of the right part.]
The motor assembly and switch are not sealed, and do pick up dirt. Its only a matter of time that with use, it will foul the switch, and dirty the armature leading to friction overheating or even permanent damage from abrasions. The intakes on the bottom of the tool are particularly easy access for metallic dust or particule from dry wall.
No speed control
Quality of motor balancing: I returned one new purchase as the motor vibrated worst at 15,000rpm. Vibrations wear the rotor, stator, bearings or mounts prematurely, overheat the chassis which potentiates failure of the electronic switch, and make precision cuts impossible. The quality of the motor is high, but it requires proper post-assembly balancing by the factory.
Clean the tool before putting it away after use, particularly when used for sanding, grinding or cutting. Just run it on full power and burst compressed air into the vents. Worse case, full disassembly for cleaning will give the best results particularly if you notice it running hot sooner than in the past.
Dremel's speed controller switches fail more than the simple switch. If cleaning doesn't work, it needs to be replaced. Internal controls are mounted inside the Dremel housing and depend on the units fan to cool. if the Dremel motor picks up grit, heat build will affect the motor and the switches capacity to cool, even with the fan working and vents are clear. The electronics normally operate with some heat, so if the ambient temperature rises, the electronics get even hotter, and it will shorten its useful life, if not cause it to fail.
So, the 100 lack of speed control isn't such a disability. If electronic switches fail, the unit may not start at all.
For bench work, its better for longevity to use an external speed control that can be kept clean, and cooled independent of the Dremel like a variac. Avoid rheostats, which simple take up the excess power and will get hotter the less power is delivered. Variacs are non-electronic adjustable transformers that reduce output voltage and thus, speed. Well made variacs are robust and last a lifetime, if not abused.
A cheap option is a triac based light dimmer, like Lutron Credenza. It has a power on LED, quality construction [made in the USA, in St. Kitts!] and since its removeable, you can add it only when you need speed control.
Keep the Dremel cool and clean, and check the brushes before each project. It should last for a very long time.