Strike indicators have received a great deal of attention from the angling media in the past few years, some negative as well as positive because they transform dead-drift nymph fishing into a relatively easily accomplished tactic.
Strike indicators are not Floats as some would suggest. Strike indicators do only what the name implies: indicate the fish's take. They can be so small that they usually cannot suspend the bait, lure, or fly. They are so small that they create no resistance to the fish when it takes the angler's offering and  boy! are they effective.

The indicator not only helps see the take, but because the fly is so small, can also act as a bobber to hold the fly at the correct depth. Indicators can make the difficult easy and the impossible at least probable. For the angler who fishes dead-drift, they are a MUST

"You Can't Catch What You Can't See" first hit my ears in the early ninety,s , I struggled all morning fishing the upstream nymph  while a future international  showed the way.  At lunch  he suggested that I use a strike indicator.  An expensive morning of casting and cursing was replaced with a brilliant afternoon of catching, releasing and enjoying life on a wonderful trout stream.                                                                                                                                                
That one "suggestion" sent me on a frustrating journey searching for that one strike indicator that would be, for me, a keeper.  I tried everything.  Foam strike indicators (riverside garbage), balsa strike indicators, feather strike indicators, plastic strike indicators, coloured tube strike indicators, a big dry fly as an strike indicator and yes, even yarn indicators.  Knitting yarn strike indicators, Egg pattern yarn strike indicators,  any yarn I could find I made a strike indicator out of it and went to the river.
NONE OF THEM FIT THE BILL.  All the while, it was getting harder and harder to see the strike, days of catching and releasing were again replaced with casting and cursing.  Getting away and spending time on a tranquil trout stream is soothing and enjoyable, but most people who go fly fishing do so to catch fish. 
If the catching wasn't important, why do you need to spend up to £1000 for a rod and reel, not to mention the cost of lines, leaders, tippets, flies, enough already.  This is why I say that a quality strike indicator is a Necessity not an Accessory. The fact is that you can (and will) catch more fish with a strike indicator than without one.  Even if you are "over 30".
FINALLY, it dawned on me.  Do it yourself.  The right strike indicator for me (and you?) was a NECESSITY not an Accessory. 
 I searched high and low, long and far.   I found it.   Yes,  HIGH IMPACT POLYSTYRENE!