In the Name of Allah, most Compassionate, most Merciful

The Prophet P.B.U.H told the immigrants to remember Allah and he recommended they count their tasbeeh on their fingers to get a higher reward...

The Prophet (peace be upon him) commanded them (the women emigrants) to be regular (in remembering Allah by saying): "Allah is most great"; "Glory be to the King, the Holy"; "there is no god but Allah"; and that they should count them on fingers, for they (the fingers) will be questioned and asked to speak.
Sunan of Abu-Dawood Hadith 1496 Narrated by Yusayrah, mother of Yasir

I saw the Apostle of Allah (peace be upon him) counting the glorification of Allah on fingers. Ibn Qudamah said (in his version: "With his right hands".)
Sunan of Abu-Dawood Hadith 1497 Narrated by Abdullah ibn Amr ibn al-'As

We should endeavor to copy the sunnah of the Prophet (P.B.U.H) because his example will not lead us astray.  It appears that later the Companions did not like to do anything other than the Prophet (P.B.U.H) and they disliked to choose the beads over the right hand when someone better prefered to use his hand.

One of the biggest arguments against prayer beads by some scholar is that you may just use them as you are doing things rather than fully concentrating on your praises of Allah.  However if we read Quran and hadiths (below) we see that remembrance of Allah is not something you do now and then in a fancy outfit, it is something you must strive to do every moment of every day!

the '...remembrance of Allah is the greatest thing in life, without doubt.'' Qur'an 29.45

O you who believe! Celebrate the praises of Allah, and do so often...Qur'an 33.41

They asked, "Who are these exceptional people (Mufarridun), O Prophet of Allah?" He replied, "Those men and women who remember Allah unceasingly." (Muslim) These are the people who are really alive.

"Remember me, I shall remember you." Qur'an 2.152

'Ali b. Abi Talha relates that Ibn 'Abbas said, "All obligations imposed upon man by Allah are clearly marked and one is exempted from them in the presence of a genuine cause. The only exception is the obligation of dhikr. Allah has set no specific limits for it, and under no circumstances is one allowed to be negligent of it. We are commanded to 'remember Allah standing, sitting and reclining on your sides,' in the morning, during the day, at sea or on land, on journey or at home, in poverty and in prosperity, in sickness or in health, openly and secretly, and, in fact, at all times throughout one's life and in all circumstances."

I have heard some people wear them as necklaces, which isn't necessarily a bad thing as Aisha (R) and Ali (R) both had bead necklaces but they didn't use the bead necklaces to do dhikr.

The people who get distracted and forget while doing dhikr can do the same with dhikr as if distracted during Salah (prayers).  One can redo the part of dhikr they get distracted upon.  There is no problem in doing extra dhikr cause of distraction, because the one purpose Allah created the jinn and mankind is to worship Allah.