I want to install frame sliders
The short answer to the frame sliders question is NO.
If you're a curious type, dissatisfied with that beautiful, concise answer, then read on!
What frame sliders are
The original design concept was to protect the really expensive bits: the engine casings and exposed parts of the frame. Here is a photo of a frame slider and a few examples of them installed where they are actually needed:
What frame sliders are not
Some people have the misconception that they're designed to protect fairings. Often, quite the opposite is true. If attached incorrectly, the frame slider's mount can shift, causing cracks in the fairing. The racers, who originally started using frame sliders, are least concerned with the appearance of their machines. Compared to custom-made hard parts that they use, plastics are cheap.
So, does the EX250 need frame sliders?
NO, it does not. Why? First, the EX250's frame is protected by plastic fairings. No part of the frame is exposed, and the engine does not protrude, so there is nothing to protect! Second, there are no good places to mount frame sliders. The only place that has been found so far is the coil bracket (durability questionable). You'd have to drill a big ugly hole through the fairing (the very thing you think you're trying to protect).
They look cool, and I still want them!
If you really want frame sliders on your EX250, they CAN Be installed. Their usefulness is unproven, and they are considered by many as purely cosmetic.
Someone posting under the nom de plume "Mibgebert" appears to be the only person who has gone through the trouble of installing frame sliders on an EX250. His design has some obvious flaws, though. The sliders are manufactured from solid steel and have sharp edges. They will not absorb any shock, and will transfer all the energy directly to the frame, potentially doing more harm than protection. Also, the sharp edges may not slide well, "biting" into asphalt and acting as pivots, again causing damage. To some extent these two issues can be corrected by adding plastic(?) tips for better energy absorption and sliding.
Here are some photos of Mibgebert's frame sliders:
This design generated some controversy. Here is a link to the original discussion.
If you're thinking about protecting your plastics with frame sliders, remember that stock turn signals will come in contact with the ground first, cracking the fairing. Replace them with flushmounts. Note that frame sliders can pose a danger if installed incorrectly. They can potentially bend your entire frame in a crash. The frame is designed to withstand certain forces, applied in certain directions at certain points. Load-bearing parts of the frame (e.g. engine mount points) are very strong, but other parts are weaker.
If you simply bolt a frame slider to a random point on your frame, all the energy of a crash will be transferred through the slider to that point. Is the frame strong enough to absorb all that energy? Will it bend? Will your mount point break off? Remember that the EX250's frame was never meant for frame sliders, and the above mentioned designs are unproven. Think before you install.
I want sliders to protect the plastic bodywork
If you are a new rider, then your best bet would be simply removing the upper fairing while you're learning to ride. Put them back on in a few months, when you get over the most common mistakes and will be less likely to drop the motorcycle.
Here is a photo of a rider in the learning stage on a fairing-less EX250:
Other devices not to be confused with frame sliders
Crash cages (this IS designed to protect plastics):
I absolutely hate frame sliders
Forum regular Craig, who is a long-term racer and track day teacher, has a few opinions on the subject:
There are times when sliders do help. In driveway tip-overs and low speed crashes, frame sliders can reduce the amount of damage. But even with sliders in place, bars still get bent/broken and bodywork still gets scratched. To me, less-scratched-up bodywork is not a big bonus.
The downside is if the bike has any momentum and that slider catches on a curb, pothole, dirt, etc... then it can start flipping, doing major damage.
Plus, if I am taking a tumble, there are already enough sharp parts sticking out without adding two big solid spears. I'd rather have a nice big plastic panel land on top of me than one with a firmly mounted spear sticking out of it.
Here are a few photos I took of a bike that had an easy low side and then slid off the track into a big, smooth, flat dirt runoff area.
Everything was fine until the frame slider dug into the dirt and started the bike flipping. The frame slider broke the case as it tore off. Also notice the bent forks and shattered rear wheel. Another bike crashed in the same turn and only needed a new rearset and clutch lever to be back out later in the day.
The rider was actually in good spirits after the crash. It was an easy lowside, and he didn't even get a bruise. He seemed to enjoy all the attention his bike was getting, but that might not be the kind of attention you'd like.
We have been keeping statistics on bike crashes at the track for the last few years, and bikes with frame sliders are more than 3 times as likely to suffer major damage than bikes without.