I have had worse luck having a fishy friend feed my tanks while away than just leaving them up to a week. This summer I left on holidays and did not feed for 10 days and no lose at all. The feeders scare me.
psyche:
Calibrating should be doable, I agree but, if I can same the money....
I like feeding my fish everyday; seeing how they get excited to see me as I approach the aquarium, around their feeding time. I guess it's nice to see anyone getting excited to see me, even if it's because they are getting something from me. LOL
i use feeders to feed my tanks.
the big thing is to get used to them so you can eyeball a consistent amount.
clumping food isn't an issue unless you put it directly over an airstone/spray bar or filter return or maybe in a hood.
i love my eheim because i can set a good schedule and it stays that way.
that being said the cheapies at walmart (penn plax daily double) can be found for around $12 and will work just fine for your 125. you can also find them at petco for probably around $30.
the thing to keep in mind is the grain size of the food you put in it. for example if you put granules in there it most likely will just pour food unless you get the expensive eheim and keep it almost closed. if you use large flakes most likely they won't pass through most feeders. you'll have to find a happy medium.
i, personally use a wide variety of food in mine. anything too large i break up. anything too small i keep in check by using smaller amounts in my mix. with this approach i am able to feed any dry food available on the market. i do mix a few months worth of food at a time but obviously that won't be necessary for your purposes.
i use them both for everyday feeding and they work fine for my purposes (to keep my heavy hands out of the cookie jar).
when acclimating yourself to your new feeder you don't want to test things in your tank. if you go with the eheim it's as simple as putting it on something it'll hang over the edge and putting something to catch the food underneath like a plate. for the penn plax you'll want to attach it to the side of a cardboard box or such with a vertical wall like an aquarium.
this will give you the chance to do a couple "dry runs" to get a feel for things. if you pinch by feel you can run them to drop in a sandwich bag. then you tip everything into the corner and give the amount a pinch to get a feel for how much you're getting.
with the eheim you just push a button and voila... feeding commenced. for the penn plax you will want to slowly turn it click by click to get a full rotation and be sure things fall into place as they would if rotation took 12 hours (which they're automatically set for). that will give you a much better idea of how much you will actually get.
neither will feed the exact amount every time. for this reason you will want to do a few extra dry runs to get an average once you think you're set.
another thing to keep in mind is they work similar to a front load washer. you will not want to fill them to the brim. rather consider somewhere between 1/2 to 2/3 to be completely full to allow space for things to turn over and fall into place.
now if you are comfortable not feeding your guys for your time away (which i also will vouch for is absolutely fine) then all this info is absolutely unnecessary. if you are paranoid like me it's a great way to keep your (seemingly intelligent) friends from killing everything in your tank.
another note: if you go with the penn plax be careful of the 3 tabs when you take it apart to fill it. they are not flexible for the most part and if you put too much stress on them they will for sure break. they still stay together well and work well after a tab has been broken and really it only makes it easier to refill them, but it happens. all in all for short periods like a vacation i still recommend the penn plax because it's absolutely not necessary to spend the $40-$50 for the eheim for a week or 2 a year. and by all means get it at walmart. it really isn't worth it to get it at a pet store.