[General Questions and Answers] Matchless 2015:
Here are the steps I followed after some extensive reading of other peoples methods and trying every possible app that would not work:

How to install TWRP and root the Samsung Galaxy J1 Mini (SM-J105F)

The device is powered by a Spreadtrum chipsets and Android 5.1.1

Basically what you need to do to root your Samsung, is to install/flash a custom recovery such as TWRP, which other than the limited functions of the OEM recovery, has all the features you need to flash a custom rom. You then boot into this TWRP recovery and use the touch menu to install/flash the SuperSu xx.zip file to give you root. It seems that other methods to root do not work on this specific phone.

Here is an Odin3 flashable *.tar md5 TWRP file that will also make it possible to root your Samsung Galaxy J1 SM-J105F, unfortunately it has to be paid for. Find it here: http://www.saroms.co.za/product/samsung-galaxy-j1-mini-j105f-root-file/ - and follow the bellow steps to flash the TWRP custom recovery and after rooting your J105F Samsung Galaxy J1 Mini.

Note: Odin3 only flashes with xxxx.tar or xxxx.tar.md5 files. TWRP can also flash xxxx.zip files.

To get into Odin mode or Download mode on the phone, switch off phone and unplug any cable to your PC or charger. Now hold in the Home button, the lower part of the volume button (V-) and the power button simultaneously. The phone will boot into a recovery screen and if you push the top part of the volume button (V+) you will switch to the Download screen. Only now can you plug your phone into the PC and run Odin3

Once TWRP recovery has been loaded, do the following to boot into TWRP recovery: Disconnect any cables to charger or PC. Switch off the phone. Now hold in the Home button, the upper part of the volume button (V+) and the power button simultaneously. The phone will boot showing the Teamwin screen and then the menu buttons which work from the touchscreen.

If you do not want to pay for the correct TWRP recovery for your specific device, then use Google to search for the file: TWRP SM-J105H_F_M_Y 5.1.1.tar

1.	Download the following files:

(i)	OEM Samsung firmware for your phone in case you have to fall back and reinstall the firmware i.e.

XFV-J105FXXU0AQA3-20170329071250.zip

(ii)	TWRP SM-J105H_F_M_Y 5.1.1.tar or any other custom TWRP recovery file for your model phone.

(iii) UPDATE-SuperSU-v2.79-20161211114519.zip

2.	Go to Settings > About device > Software Info > and tap on Build number a few times until you are a developer.

3.	You should now see and tap on 'Developer options' if you go back to Settings.

4.	In Developer options. turn on 'OEM Unlock' by moving the slider to the right, Enable. Never set that setting to off once you have loaded a custom firmware or TWRP custom recovery! You phone will brick and only show *“Custom binary blocked by FRP lock” after the next reboot!! (FRP = Factory Reset Protection)

* If so install OEM firmware with Odin3 and start again.

5.	Copy the UPDATE-SuperSU-v2.79-20161211114519.zip file to the root of your internal storage SD card (not external). This will be installed by using TWRP recovery. Use your PC to do this.

6.	Turn the device off and boot into "Download Mode” (V- and Home and Power ... and then V+)

7.	Run the Odin3 application on your PC and load the recovery *.md5 file under 'AP' or load the file: TWRP SM-J105H_F_M_Y 5.1.1.tar.

8.	Connect the MS-J105f to your PC and let Odin3 connect and ID:COM will go blue and show i.e. 0 : (COM4) > then click Start.

9.	The SM-J105F will power on when done. Disconnect cable and power it off again.

10.	Boot into recovery (V+ and Home and Power) will now boot into TWRP.

11.	You will now see the TWRP menu touch screen.

12.	Tap Install > scroll to the "UPDATE-SuperSU-v2.79-20161211114519.zip" file you downloaded and copied to the phone memory tap it.

13.	Swipe at the bottom slider to confirm install.

14.	Tap Reboot to system when done and you should be rooted.

15.	Install and run SuperSU from the app store and run.

16.	Install and run Root Checker Basic.

To reinstall the OEM firmware, download the proper xxxx.zip from the Samsung website.

You must the extract the xxx.tar.MD5 file from the download

If you can get into the Download screen on your SM-J105F then use Odin3 as above, just under PA select the OEM file xxxx.tar.MD5 (it takes a short while to select properly as it a very large 2 gb file after extracting)

Hope this helps someone else. Thanks to all whose posts and contributions helped me.