My interest was to have a unit to train on bass, that is able to:
Play original songs / pre-recorded to wav or mp3
Playing over a original / pre-recorded
Playing a slow song
Playing a looped portion of a song
Register on bass
Register on bass over a original / pre-recorded
All in the headphones / amp to a external
Zoom H4N adequacy for this purpose:

Play original songs / pre-recorded to wav or mp3
Ok but the photo does not show the long names of files transferred from a PC. And we must meet the rigid structure of directories.

Playing over a original / pre-recorded
Ok with the Monitor ON

Playing a slow song
Ok, from 50% to 150% with retention of its original height, but a specific mode of reading is incompatible with the looping of a portion of the song.

Playing a looped portion of a song
Ok, but a specific mode of reading is incompatible with the slow motion / fast.

Register on bass
Ok, since input or microphone input 1 or 2

Register on bass over a original / pre-recorded
Ok, but in multitrack and must be assigned to one or two of the original song 4 tracks / pre-recorded (mono or stereo), only to wav ...

All in the headphones / amp to a external
Ok via the jack line out / headphone

The likely benefits of Tascam GT-R1 for this purpose:
Ergonomics simpler and more suitable
Consideration of tags files
Changing the height of a piece
Beatbox
Plus Size contained

Specifics H4N Zoom:
6.35 2 jack / XLR for guitar / bass in / line in / mic in / ... with phantom power 24V/48V
Built-in speaker
Multitrack, music editing option
Serves as an audio interface 2 inputs / 2 outputs 44.1kHz or 48kHz via USB
Food provided, also runs on batteries
Thread for screw-type bracket with camera
Conclusion
I hesitated with the Tascam GT-R1 and decided for myself that that was more professional. Well, after several days of discovery / use, this device is certainly not the most suitable for my initial needs. I'll still keep it because it is very good at recording and it could serve me too!