I agree, however you will need to get up to speed faster, as you need to have the same avarage speed. As you start from 0 and you need to get up to speed faster and your maximum might need to be a bit faster.
All together you will get more rest, as the rest period is 18 over 25 meters, which is 1 second more than 35 over 50 meters.
Interestingly, for women this test has become harder. As they now have 17 seconds over 75 meters, where they used to have 35 seconds on 150 meters. Both in terms of speed and with the before mentioned startup speed, they will find this test harder.
Good idea. As you noted, these tests are a mental thing. I have run the FIFA (modified in Norway though to be 26 instead of 20 intervals) two times a year for 6 years now. It is the newbies that tend to fail or struggle. At around 10-15 intervals they struggle mentally. It is where the experienced referees steps in and motivate them to get through it. It is quite nice actually, to see how referees help each other out. Runners who swore they were ready to quit manage 10 more laps and are so greatfull afterwards.
To make sure I am both physically and mentally ready, I run the test on a treadmill every week. I run 30 seconds at 18.8 km/h, and rest standing still for 31 seconds. That puts me well over the requirements. The nice thing about this is, when the test comes I have the confidence to know I will pass this without problems.
I have had a go on grass of the test and it is certainly a test! Did 30 intervals solo on quite a hot evening and it is not fun.
Getting up to speed was not an issue, but getting into a running rhythm was more difficult than the longer version for some reason. Also the test is long and the prospect of 40 intervals is demoralising. Also 20 seconds rest flies by!!!
It was less fun than 150m. but will try it again next week a little better prepared.