If you're looking to prepare for Baro's "everything goes" sale during Tennocon, you can access my complete list of recommendations HERE.
Recommendations:
Mods
Primed Reach
+3 (meters, I guess) of melee range. A massive improvement over the normal version, and great for any normal melee weapon. (It doesn't work for special stuff like glaive throws and gunblade shots.) Get it as soon as you can.
Split Flights
Up to 400% multishot (and -720% accuracy) on scoring hits for (non-explosive) bows. Mutually exclusive with other multishot mods. Only viable on the Cernos Prime and the Mutalist Cernos, but it makes the latter excel. Only get this if you like those two weapons.
Primed Cleanse Corrupted
+55% Damage vs. Corrupted for Pistols. These anti-faction mods provide respectable boosts, especially since status effects double dip on them. But in normal play, they require too much micromanagement to be effective. However, there are a few endgame activities which specifically involve Corrupted, such as Conjunction Survival, Steel Path Void Fissures, and to a lesser degree, Necramechs on Deimos. If you're planning to engage with these activities, and have the budget to max out this mod, it makes for a good investment.
Weapons
Baro's weapons typically fall into low A or B rank in tierlists, so DE at least tries to justify their asking price. And even the trashiest of weapons are worth buying if you need the Mastery Rank they provide. Or if you have good riven for them, since their disposition is usually quite high. On the other hand, Warframe has a massive arsenal, and for every weapon Baro sells, there's gonna be another that can do the same job just as well, or even better. In that sense, everything in here is "safe to skip."
Halikar Wraith
A glaive with good base stats, but unfavorable damage types and a pointless gimmick. (You know what's better than disarming your enemies? Inflicting on them massive slash procs that sap the health of anyone who survives the initial explosion.) It's good, but there are better glaives out there.
Mara Detron
A secondary shotgun. While outclassed by its Tenet variant, it's still a powerful weapon with good stats and easy handling, albeit annoyingly frequent reloads. If you don't like hunting Sisters, it's an easy recommendation.
Cosmetics
Scoria Diadem
New! A facial accessory for the Operator/Drifter. Putting a precious gemstone into you third eye socket is such an anime thing to do.
Hydroid Immortal Skin
Base Hydroid isn't the best looking frame, and this paintjob doesn't help much.
Prisma Daedalus Armor Set
A Prisma-infused version of the plat-only Daedalus set. The shoulder and knee plates stick out and away from the frame's body at an awkward angle. I think this makes for poor Fashionframe, but you might disagree.
Ki'Teer Syandana
Who thought something so angular and geometrical in pictures can be so floppy and rubbery in reality?
De Nas Pistol Skin
A very sleek and fancy skin for your pistols. Can go well with more gnarled designs, like Oberon Feyarch and Titania Empress.
Sonicor Elixis Skin
The Elixis skins cover most of the weapon in a uniform coppery/metallic texture with the occasional grid of triangular indentations. Does not always look good, but always look shiny.
Ki'Teer Earpiece
A pair of Ki'teer-themed earrings for your Operator.
Ki'Teer Moa Pet Skin
If you don't like the bulky, exaggerated style of the original parts, this one provides a sleek, stylish makeover for your favorite robotic dinosaurs.
Liset Cydonia Skin
A landing craft skin with the same theme and color scheme as vanilla Inaros.
Odonata Elixis Skin
The Elixis skins cover most of the Archwing in a uniform coppery/metallic texture with the occasional grid of triangular indentations. Does not always look good, but always look shiny. Then again, if you have the money to buy this, why are you still using the Odonata?
Noggle Statue - The New War Veso-R
Bobblehead of Veko, the unsung hero of the New War.
Telamon Dance of Death
Yet another Leverian-related Orbiter decoration. This one is a bust of a Wukong main expressing their feelings over the Great Ammo Nerfs of 2022.
Deimos Lobotriscid Prex
Prex cards depicting Deimos-associated entities. These were given away like candy during the Heart of Deimos update. If you haven't got them then, you can get them now for a modest price.
Parazon Poster
A cool looking poster. Presumably holographic, because it's infinitely thin and floats a few centis off the wall.
Ki'Teer Tribute Glyph
Do you really want to pay Baro just to serve as free advertisement for him?
Fae Path Ephemera
One the older step-Ephemeras, and rather insubstantial compared to, say, Eros Wings or Vengeful Charge. A permanent fixture of Baro's repertoire.
I might have sharp and opinionated remarks about these items, but I'm not the fashion police. Buy whatever cosmetic tickles your fancy!
Other
Grustrag Three Beacon
Getting marked for a G3 spawn is easy. Actually getting them to spawn is a painful waiting game. While their dedicated weapon drop is superceded by its variant, you might still want it for the MR -- or you want the Landing Craft part only the Grustrag 3 can drop. This thing helps to summon them to a location of your choosing. I suggest using it in a keyshare, so you get 4 spawns from 1 beacon.
If you haven't played Sands of Inaros yet, buy the quest key and do it (and bring your best setup for scanning Kavats). If you have Inaros Prime, you can buy the Baro Void-Signal (one per visit) to access some special cosmetics.
Also, check the answers below for second opinions.
Monke