I own NLU, FLU, BLU, BLU+.
For the most part I use an NLU, then an FLU, and lastly the BLU (or BLU+). This is my bias, and each to suffer their own.
An NLU with a glass screen protector gives a great display (very clear). An NLU, is under rated and a great buy. The only limitation is lighting, but do you only want to play / use, in low / no light (which is bad for your eyes in any case). If you like to emulate Gameboy, this unit is great (I am surprised that Nintendo Gameboy fans over look this device).
The FLU is the best all rounder night and day. The light transmitting screen does affect the clarity (but it is slight). You can switch off the light and use like an NLU, in normal light. Depending on the kwality of the fitment there may be some errors in the light transmission (you get used to it over time).
The BLU (and BLU+), is great for no / low light. You can like the FLU, turn the light off, but the screen is then very, very dull, and you will generally keep the light on (unless you listen to MP3 files). The screen display is bright, and the colours are vivid (expect some herring bone interference patterns on the display, this is normal and you don't notice them after a while). You may see some ghosting too (which is trivial).
More important than what unit to buy, is the condition the sold unit is in. You can follow a members advice to get a certain unit, and find yourself with a real lemon. Study the picture (or if not sufficient, request some more images). Shiny buttons indicate a lot of use (not always bad). Study the stick position the nearer to central position the better. Even though the screen protectors are replaceable you would rather not, so look for a clear screen, with next to no scatches to the tinting. Look for obvious signs of wear and damage, units are often dropped, and get scratched up. Make sure that the unit you buy has at least one card with it (**IMPORTANT**). Try your hardest to get a unit with next to no use (as indicated by the seller).
In the case of ebay check the sellers rating, never buy fom a seller with less than 98% rating. Always check that the item is not "no returns". Check to see if the payment for return postage is refunded if the item is indeed faulty. Always buy with paypal (even though the credit shows in the sellers account, paypal hold on to the money for 21 days - in case of refund).
Once you have your unit test it with fresh cells. If there is any cause for dissatisfaction of the purchase return the item immediately, and get a refund through paypal (the seller has no choice but to oblige).
If happy with the unit, get a damp cloth and give it a clean (you want to remove as much of the previous owner as you can - they can be quite stubborn). Pay close attention to the battery cover check that the "clip", is not cracked, if so super glue. Also there will be superficial cracks in a few place, I superglue, then rub down. The key caps on one of the buttons may have failed you may want to source replacements, or fabricate your own from what you have at home (i.e. I use Gamecube joypad parts - modified).
When the unit has been all cleaned up you can then proceed to setting the unit up. Back up the card(s) that came with the unit. On the older units (i.e. not BLU), the freelauncher was used. I replace all of these with "Slubman". From the GP32 section download the flashing software, and the firmware of your choice, on one of the cards that came with the unit, with enough room (both files are small - you may need to delete a game file or ROM to make space). Put the flashing software named "FW.FXE", in the "GPMM" folder. Then put the chosen firmware renamed "FW.(BIN)", in the root directory. You can run the firmware flasher, and follow the prompts (make sure the cells are fresh).
You may want to purchase additional SMC cards. I format the cards with the GP32 first, then with a card reader transfer files from the PC. Labels on cards are a good idea.
The main reason I use an NLU, is because this paticular unit has the best feel (out of 11 GP32 units I currently have), as every unit has a different feel. You will, and do get used to yours, but given the choice I always like to use the unit that has the right feel of the controls for me, never mind all this BLU+ is best. A point proved when I gave an NLU, to someone (to demonstrate a game), who then wanted a back lit display, so I then gave the BLU, then to be told the display was clearer on the NLU, and the controls were better too (which is why I gave that NLU unit in the first place).
