After a few weeks travel to Malaysia, Turkey and Greece, started to look a bit shaggy and so bought some hair clippers. These cost €10, and so paid for themselves with one haircut. I didn't take my electric hair clippers on a trip as they are mains powered and would be difficult to use in hotel bathrooms (especially where these were shared).
There are a bewildering range of hair clippers, beard trimmers and dual purpose shavers for cutting hair. The mains powered hair clippers tend to have several attachable guides for different length hair, whereas the battery ones and beard trimmers have adjustable guides built into the clippers.
The units with attachable guides generally to have guides for longer hair: up to Number 4 comb (.5 inch or 13 mm). The hair clippers units with built in guides and the beard trimmers cut to 7 mm or less. Also the beard trimmers are narrower and so cut a narrower strip of hair.
I ended up with the Zowael ZRC-009 hair clippers, which are rechargable and cut from 1 to 7 mm, with a built in guide. They are not perfect, particularly in not being waterproof. Also being rechargable is a disadvantage for traveling, as I either have to carry the charger (and an adapter for the local power), or hope they have enough charge to last the trip (the manual claims one hour's cutting on a full charge). I couldn't find this unit on Amazon.com, but it appears similar to the unfortunately named Scalpmaster Pro Cord / Cordless Rechargeable Professional Hair Trimmer. These seem to contain an AA size rechargable battery and a simple charging circuit.
I would have preferred a set of battery clippers, which can use either disposable or rechargable AA batteries. The best I saw was a Phillips battery powered beard trimmer for about €15 duty free. But I then could not find a set outside the one duty free store (the other stores only sold more expensive rechargable units). There is a similar, but higher priced, rechargable Philips Norelco Multi-Trim All Purpose Groomer.
There are a range of all in one combined hair and beard trimmers offered. There seem to be few combined shavers and beard trimmers, as these functions are not necessarily compatible (hair clippers will not give a close shave and will tend to uncomfortably scrape the skin). One brand of clippers suggests these can be used to cut the beard to a three day growth, which should work okay.
Looking on Amazon.com, one of the more odd items I noticed was the "MANGROOMER Do-It-Yourself Electric Back Hair Shaver". This appears to be an electric razor on a long folding handle, so it can reach the middle of your back.
Another odd unit I saw in the duty free store were the Philips Norelco Accu-Vac Beard and Moustache Trimmer. This has a small fan and air filter built into the body so it vacuums the cut hair off the face. While cutting hair can be messy, this does not sound a good solution. The unit is much large than others, due to the need for the fan. Also you would have to empty and clean the hair from the unit.