As for film development I use a Jobo and always use the same thermometer. Many a printer finer than most of us had their own systems and did wonderful work without this device. Its one of those things we all want but can do without in my opinion...
By "this device" are you referring to the Zone VI timer or the Jobo?
I refer to the compensating timer. Of course the Jobo is also just an added advantage that one could do without. What I am getting at, is what most of us would admit. Using standard methods and materials with competence procedure can get the best out of our film and prints if we become 'expert' in our individual methods and standardize we can tweak til the cows come home.
All the other devices and gizmos can make it easier or more difficult. I sometimes suffer from just plain lack of basics and my time in the darkroom is totally frustrating and wasted. I remember once spending 4 hours trying to get just one decent print and cursing my papers, and testing for basic black and safelights etc. when I finally realized that I was just cheap and had re-used exhausted developer. I don't know how equipment can override brain farts. At least not yet...
my work around - compensating darkroom guy, not timer
I have hijacked an old Kodak film development dial calculator, and re-purposed it for paper.
I have a dial calculator thingie that came in a mid 80's kodak darkroom dataguide - It is called a development dial. The other side of the dial is an enlarging dial - also a handy dial computer.
On the development side, basically you work out what your best film processing time is and look at the dial for the temp and time combination - that equates to a single development number. The dataguide has charts to suggest the best development time in terms of developmen number to start with. It also has percentages on the dial so it is easy to work out n+1 push time, or n-1 pull time when developing sheet film.
The next time the film and developer come together, set the development number, and look at the time that corespomds to the temperature you want/have. Set the timer to match, and a way you go.
I have extended the idea ( and in some cases the scale on the dial) for paper development. I try to standardize on a paper and developer combination - like say dektol/agfa100 at 1:2 20C 2' for RC - maybe 3' for FB ( i would have to look to my notes). That combination equals a development number on the dial calculator. I use 20 minutes and divide by 10, because the dial scale from Kodak doesn't work very well at 2'.
But life doesn't always work at 68.
Say I am printing once the kids are in bed and my wife has on 20/20 which I can't stand on a friday night. The session is going well, and the room and tray etc are at say 68F/20C (I wish it was that warm down there some days). But I am tired out by the week, and it is midnight. So I drop saran wrap over the trays and head to bed. The next morning I am up at the usual 6am (I wish I could convince my body to sleep in on weekends). No one will be going anywhere til 10am. A few hours of darkroom time!
Back in the darkroom the chems in the trays are a chilly 62F. No priblem (apart form cold fingers) Look at the development dial and compute the equivalent to 68F 2' time. Reset the timer to this new time, and check the temperature after half an hour to see if your fingers have warmed the solution, and you can set the timer for less time to develop a sheet for standard development.
Note - don't do this with developers that include glycin. I actually try to do ansco 130 etc at about 75F. My solution in this case is to stick the tray itself, or a jug into which the devloper has been poured, and pop out into the laundry room to 'my' microwave, and warm the solution for 20 seconds or so. If I heat it abouve my target temperature - no priblem - look to the development number dial calculator and see that - ah , for example, I should be developing for 1'40".