I have a later reiteration of etrex and GPS phones don't compare in accuracy and locking onto the signal.
All the phones I've had over the last 5 years, or so, have had excellent accuracy. And, with the added clues the latest phones get from WiFi access points, the time for first lock is often much better than my (admittedly old) eTrex.
I find my phone great for intermittent mapping usage. If I'm lost in London, or confused in the countryside then I have mapping apps for both situations. Being able to carry 1:50,000 Ordnance Survey maps of the whole of the UK, and 1:25,000 for much of it, is extremely cool.
But using GPS for logging really does eat up the battery. Yes, power packs will work - if you remember to plug the phone in when it's needed. When I'm on holiday I don't want to be bothered by gear - I want everything to be plain and simple.
My BGT-31 is small (but not so small as to make it unusable - maybe 1/3 the size of my eTrex). It's sensitive (no problem keeping track in its case, in a bag, in a bus). And it's got great battery life.
At the start of the day I switch it on, put it at the bottom of my bag and forget about it. At the end of the day I put it on recharge. If I forget, no problem - the battery will keep it going for over 48 hours (and that's without putting it into battery-saving mode). At the end of the trip I just download the various data files, translate them to .gpx and tag all the images.