My favorite flashlight is BY FAR this one:
https://www.amazon.com/Hausbell-Ultra-Bright-Flashlight-Tactical/dp/B00CEOII9K
I've got $300 surefire flashlights, several high end tactical lights, I keep a Fenix E12 in my EDC, LED lanterns, headlamps.... too many damn lights, really.
Yet, this cheapo flashlight is just rock-solid. The single best thing about it is that it's basically a throw away loaner. When I go camping with lots of guys or kids, someone always needs a flashlight - "Here you go, keep it." I've got one of these lights in almost every drawer in my house except the kitchen drawer. On my night stand, on my desk, all over my house. I must have bought, god honestly, 50 of them. These are in every kit I own, and in some kits I have 2 of them.
If you do want to do a bulk purchase of these lights, they are on Alibaba for cheaper, around $2.50 each.
They aren't the type of light I'd want to strap on the front of my AK47 if I was in Syria, they aren't 100% dependable, but they are like a Bic Lighter of flashlights.
I tried that exact pen and found it too bulky and the light would turn on daily by just bumping the button.
Switched to a real flashlight - https://www.amazon.com/gp/product/B00CEOII9K/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
Very bright. Love the zoom. Fits easily in pocket. Love the clip on it. And it has the "tactical" points guarding the edge. Like you I find that having a flashlight on me is way more handy that I thought. And I'm a desk bitch!
There is an option on Amazon (with prime) around $4. Yes. $4.
It's got a high, low and strobe, as well as a couple of options for focusing the light.
One option is http://www.amazon.com/gp/product/B00CEOII9K/ref=oh_aui_detailpage_o08_s00?ie=UTF8&psc=1 those are the ones that can be focused to an extremely tight beam, so tight you can see the unused space in the light filament on the projecting surface. That same guy ha a ton of options.
I will let you decide for your self, OFC- but these lights cannot be beat. get a couple rechargables from the same seller and you are good!
It's a generic model on Amazon, here's a link selling the same style.
Your flashlights start at a relatively high price point. These are pretty decent, $10 for two, and take AAs or 14500s.
I got a pair of these for $10. While they are AA form factor, I mainly use these batteries for their brightness.
$10 isn't a whole lot, but a two pack of really bright yet small flashlights is a practical purchase.
2X Hausbell Mini 7W CREE LED Flashlight 300LM (https://www.amazon.com/dp/B00CEOII9K/ref=cm_sw_r_awd_xuO6ub1JK7RJN)